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 $44.95   5.258%   $47.3135   $47.31   $47.30   $47.30  
  Purchase #2 $26.76   4.727%   $28.0249   $28.02   $28.00   $28.00  
  Purchase #3 $229.25   11.553%   $255.7353   $255.74   $255.75   $255.70  
  Purchase #4 $112.30   9.778%   $123.2807   $123.28   $123.30   $123.30  
  Purchase #5 $89.44   8.699%   $97.2204   $97.22   $97.20   $97.20  
  Purchase #6 $206.51   7.289%   $221.5625   $221.56   $221.55   $221.60  
  Purchase #7 $60.32   7.343%   $64.7493   $64.75   $64.75   $64.70  
  7 purchase totals = $769.53       $837.8866   $837.88   $837.85   $837.80