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 $59.29   10.625%   $65.5896   $65.59   $65.60   $65.60  
  Purchase #2 $244.53   12.731%   $275.6611   $275.66   $275.65   $275.70  
  Purchase #3 $125.54   8.557%   $136.2825   $136.28   $136.30   $136.30  
  Purchase #4 $221.77   10.617%   $245.3153   $245.32   $245.30   $245.30  
  Purchase #5 $249.54   3.809%   $259.045   $259.05   $259.05   $259.00  
  Purchase #6 $228.77   13.701%   $260.1138   $260.11   $260.10   $260.10  
  Purchase #7 $135.80   10.526%   $150.0943   $150.09   $150.10   $150.10  
  7 purchase totals = $1,265.24       $1,392.1016   $1,392.10   $1,392.10   $1,392.10