Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $156.50   12.206%   $175.6024   $175.60   $175.60   $175.60  
  Purchase #2 $129.59   11.804%   $144.8868   $144.89   $144.90   $144.90  
  Purchase #3 $219.34   13.809%   $249.6287   $249.63   $249.65   $249.60  
  Purchase #4 $211.29   13.746%   $240.3339   $240.33   $240.35   $240.30  
  Purchase #5 $151.50   6.450%   $161.2718   $161.27   $161.25   $161.30  
  Purchase #6 $169.91   10.621%   $187.9561   $187.96   $187.95   $188.00  
  Purchase #7 $226.94   12.287%   $254.8241   $254.82   $254.80   $254.80  
  7 purchase totals = $1,265.07       $1,414.5038   $1,414.50   $1,414.50   $1,414.50