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 $93.25   7.203%   $99.9668   $99.97   $99.95   $100.00  
  Purchase #2 $201.91   11.282%   $224.6895   $224.69   $224.70   $224.70  
  Purchase #3 $39.27   4.795%   $41.153   $41.15   $41.15   $41.20  
  Purchase #4 $78.49   13.167%   $88.8248   $88.82   $88.80   $88.80  
  Purchase #5 $237.68   4.618%   $248.6561   $248.66   $248.65   $248.70  
  Purchase #6 $168.46   12.358%   $189.2783   $189.28   $189.30   $189.30  
  Purchase #7 $30.89   6.614%   $32.9331   $32.93   $32.95   $32.90  
  7 purchase totals = $849.95       $925.5016   $925.50   $925.50   $925.60