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 $229.65   6.874%   $245.4361   $245.44   $245.45   $245.40  
  Purchase #2 $71.73   8.646%   $77.9318   $77.93   $77.95   $77.90  
  Purchase #3 $157.32   10.223%   $173.4028   $173.40   $173.40   $173.40  
  Purchase #4 $235.68   3.711%   $244.4261   $244.43   $244.45   $244.40  
  Purchase #5 $64.94   7.151%   $69.5839   $69.58   $69.60   $69.60  
  Purchase #6 $111.49   9.827%   $122.4461   $122.45   $122.45   $122.40  
  Purchase #7 $88.72   3.313%   $91.6593   $91.66   $91.65   $91.70  
  7 purchase totals = $959.53       $1,024.8861   $1,024.89   $1,024.95   $1,024.80