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 $52.47   12.497%   $59.0272   $59.03   $59.05   $59.00  
  Purchase #2 $128.37   7.570%   $138.0876   $138.09   $138.10   $138.10  
  Purchase #3 $159.41   12.588%   $179.4765   $179.48   $179.50   $179.50  
  Purchase #4 $166.30   13.266%   $188.3614   $188.36   $188.35   $188.40  
  Purchase #5 $51.98   12.562%   $58.5097   $58.51   $58.50   $58.50  
  Purchase #6 $230.32   13.298%   $260.948   $260.95   $260.95   $260.90  
  Purchase #7 $217.32   4.840%   $227.8383   $227.84   $227.85   $227.80  
  7 purchase totals = $1,006.17       $1,112.2487   $1,112.26   $1,112.30   $1,112.20