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 $222.59   12.633%   $250.7098   $250.71   $250.70   $250.70  
  Purchase #2 $124.52   9.175%   $135.9447   $135.94   $135.95   $135.90  
  Purchase #3 $168.92   7.352%   $181.339   $181.34   $181.35   $181.30  
  Purchase #4 $51.65   7.438%   $55.4917   $55.49   $55.50   $55.50  
  Purchase #5 $20.40   6.212%   $21.6672   $21.67   $21.65   $21.70  
  Purchase #6 $65.46   13.250%   $74.1335   $74.13   $74.15   $74.10  
  Purchase #7 $192.43   12.389%   $216.2702   $216.27   $216.25   $216.30  
  7 purchase totals = $845.97       $935.5561   $935.55   $935.55   $935.50