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 $141.35   7.386%   $151.7901   $151.79   $151.80   $151.80  
  Purchase #2 $239.25   6.396%   $254.5524   $254.55   $254.55   $254.60  
  Purchase #3 $205.52   8.378%   $222.7385   $222.74   $222.75   $222.70  
  Purchase #4 $189.95   13.258%   $215.1336   $215.13   $215.15   $215.10  
  Purchase #5 $72.67   5.102%   $76.3776   $76.38   $76.40   $76.40  
  Purchase #6 $12.91   7.523%   $13.8812   $13.88   $13.90   $13.90  
  Purchase #7 $246.62   13.380%   $279.6178   $279.62   $279.60   $279.60  
  7 purchase totals = $1,108.27       $1,214.0912   $1,214.09   $1,214.15   $1,214.10