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 $43.28   8.652%   $47.0246   $47.02   $47.00   $47.00  
  Purchase #2 $155.41   13.534%   $176.4432   $176.44   $176.45   $176.40  
  Purchase #3 $86.45   13.151%   $97.819   $97.82   $97.80   $97.80  
  Purchase #4 $47.75   5.599%   $50.4235   $50.42   $50.40   $50.40  
  Purchase #5 $210.63   4.123%   $219.3143   $219.31   $219.30   $219.30  
  Purchase #6 $107.46   9.813%   $118.005   $118.01   $118.00   $118.00  
  Purchase #7 $92.85   7.456%   $99.7729   $99.77   $99.75   $99.80  
  7 purchase totals = $743.83       $808.8025   $808.79   $808.70   $808.70