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 $58.80   13.270%   $66.6028   $66.60   $66.60   $66.60  
  Purchase #2 $137.26   10.231%   $151.3031   $151.30   $151.30   $151.30  
  Purchase #3 $139.26   3.134%   $143.6244   $143.62   $143.60   $143.60  
  Purchase #4 $26.36   11.282%   $29.3339   $29.33   $29.35   $29.30  
  Purchase #5 $85.76   13.494%   $97.3325   $97.33   $97.35   $97.30  
  Purchase #6 $201.96   10.750%   $223.6707   $223.67   $223.65   $223.70  
  Purchase #7 $88.84   3.822%   $92.2355   $92.24   $92.25   $92.20  
  7 purchase totals = $738.24       $804.1029   $804.09   $804.10   $804.00