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 $119.39   12.228%   $133.989   $133.99   $134.00   $134.00  
  Purchase #2 $48.71   9.616%   $53.394   $53.39   $53.40   $53.40  
  Purchase #3 $27.35   7.495%   $29.3999   $29.40   $29.40   $29.40  
  Purchase #4 $136.50   6.541%   $145.4285   $145.43   $145.45   $145.40  
  Purchase #5 $47.33   9.658%   $51.9011   $51.90   $51.90   $51.90  
  Purchase #6 $117.87   3.195%   $121.6359   $121.64   $121.65   $121.60  
  Purchase #7 $115.47   9.305%   $126.2145   $126.21   $126.20   $126.20  
  7 purchase totals = $612.62       $661.9629   $661.96   $662.00   $661.90