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 $112.86   12.200%   $126.6289   $126.63   $126.65   $126.60  
  Purchase #2 $87.62   12.235%   $98.3403   $98.34   $98.35   $98.30  
  Purchase #3 $112.35   11.202%   $124.9354   $124.94   $124.95   $124.90  
  Purchase #4 $62.72   13.274%   $71.0455   $71.05   $71.05   $71.00  
  Purchase #5 $189.91   8.766%   $206.5575   $206.56   $206.55   $206.60  
  Purchase #6 $209.57   11.151%   $232.9392   $232.94   $232.95   $232.90  
  Purchase #7 $14.82   4.113%   $15.4295   $15.43   $15.45   $15.40  
  7 purchase totals = $789.85       $875.8763   $875.89   $875.95   $875.70