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 $60.49   6.141%   $64.2047   $64.20   $64.20   $64.20  
  Purchase #2 $192.62   7.251%   $206.5869   $206.59   $206.60   $206.60  
  Purchase #3 $110.49   11.462%   $123.1544   $123.15   $123.15   $123.20  
  Purchase #4 $57.49   6.321%   $61.1239   $61.12   $61.10   $61.10  
  Purchase #5 $141.93   13.586%   $161.2126   $161.21   $161.20   $161.20  
  Purchase #6 $69.29   11.666%   $77.3734   $77.37   $77.35   $77.40  
  Purchase #7 $59.48   11.552%   $66.3511   $66.35   $66.35   $66.40  
  7 purchase totals = $691.79       $760.0070   $759.99   $759.95   $760.10