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 $57.28   13.740%   $65.1503   $65.15   $65.15   $65.20  
  Purchase #2 $182.51   8.389%   $197.8208   $197.82   $197.80   $197.80  
  Purchase #3 $87.69   6.776%   $93.6319   $93.63   $93.65   $93.60  
  Purchase #4 $85.62   5.622%   $90.4336   $90.43   $90.45   $90.40  
  Purchase #5 $51.63   9.425%   $56.4961   $56.50   $56.50   $56.50  
  Purchase #6 $231.79   8.706%   $251.9696   $251.97   $251.95   $252.00  
  Purchase #7 $9.56   13.838%   $10.8829   $10.88   $10.90   $10.90  
  7 purchase totals = $706.08       $766.3852   $766.38   $766.40   $766.40