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 $228.34   12.416%   $256.6907   $256.69   $256.70   $256.70  
  Purchase #2 $134.48   5.478%   $141.8468   $141.85   $141.85   $141.80  
  Purchase #3 $45.77   11.646%   $51.1004   $51.10   $51.10   $51.10  
  Purchase #4 $194.95   6.778%   $208.1637   $208.16   $208.15   $208.20  
  Purchase #5 $64.90   9.513%   $71.0739   $71.07   $71.05   $71.10  
  Purchase #6 $207.87   5.711%   $219.7415   $219.74   $219.75   $219.70  
  Purchase #7 $55.50   6.218%   $58.951   $58.95   $58.95   $59.00  
  7 purchase totals = $931.81       $1,007.5680   $1,007.56   $1,007.55   $1,007.60