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 $195.98   12.277%   $220.0405   $220.04   $220.05   $220.00  
  Purchase #2 $202.28   11.543%   $225.6292   $225.63   $225.65   $225.60  
  Purchase #3 $194.96   3.208%   $201.2143   $201.21   $201.20   $201.20  
  Purchase #4 $189.48   5.453%   $199.8123   $199.81   $199.80   $199.80  
  Purchase #5 $48.47   4.703%   $50.7495   $50.75   $50.75   $50.70  
  Purchase #6 $245.99   3.230%   $253.9355   $253.94   $253.95   $253.90  
  Purchase #7 $64.71   11.137%   $71.9168   $71.92   $71.90   $71.90  
  7 purchase totals = $1,141.87       $1,223.2981   $1,223.30   $1,223.30   $1,223.10