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 $246.60   4.199%   $256.9547   $256.95   $256.95   $257.00  
  Purchase #2 $46.39   3.537%   $48.0308   $48.03   $48.05   $48.00  
  Purchase #3 $68.31   9.253%   $74.6307   $74.63   $74.65   $74.60  
  Purchase #4 $12.56   9.657%   $13.7729   $13.77   $13.75   $13.80  
  Purchase #5 $245.98   3.606%   $254.85   $254.85   $254.85   $254.90  
  Purchase #6 $194.43   5.410%   $204.9487   $204.95   $204.95   $204.90  
  Purchase #7 $190.80   13.756%   $217.0464   $217.05   $217.05   $217.00  
  7 purchase totals = $1,005.07       $1,070.2342   $1,070.23   $1,070.25   $1,070.20