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 $222.87   6.465%   $237.2785   $237.28   $237.30   $237.30  
  Purchase #2 $33.75   4.596%   $35.3012   $35.30   $35.30   $35.30  
  Purchase #3 $97.68   11.486%   $108.8995   $108.90   $108.90   $108.90  
  Purchase #4 $43.71   9.294%   $47.7724   $47.77   $47.75   $47.80  
  Purchase #5 $39.28   12.635%   $44.243   $44.24   $44.25   $44.20  
  Purchase #6 $131.42   11.226%   $146.1732   $146.17   $146.15   $146.20  
  Purchase #7 $134.83   10.805%   $149.3984   $149.40   $149.40   $149.40  
  7 purchase totals = $703.54       $769.0662   $769.06   $769.05   $769.10