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 $59.78   9.558%   $65.4938   $65.49   $65.50   $65.50  
  Purchase #2 $50.96   13.370%   $57.7734   $57.77   $57.75   $57.80  
  Purchase #3 $10.51   4.464%   $10.9792   $10.98   $11.00   $11.00  
  Purchase #4 $182.81   3.803%   $189.7623   $189.76   $189.75   $189.80  
  Purchase #5 $228.47   11.853%   $255.5505   $255.55   $255.55   $255.60  
  Purchase #6 $97.90   6.232%   $104.0011   $104.00   $104.00   $104.00  
  Purchase #7 $237.47   9.701%   $260.507   $260.51   $260.50   $260.50  
  7 purchase totals = $867.90       $944.0673   $944.06   $944.05   $944.20