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 $147.93   11.403%   $164.7985   $164.80   $164.80   $164.80  
  Purchase #2 $25.78   5.585%   $27.2198   $27.22   $27.20   $27.20  
  Purchase #3 $119.93   11.164%   $133.319   $133.32   $133.30   $133.30  
  Purchase #4 $122.45   5.403%   $129.066   $129.07   $129.05   $129.10  
  Purchase #5 $60.33   10.515%   $66.6737   $66.67   $66.65   $66.70  
  Purchase #6 $41.95   8.279%   $45.423   $45.42   $45.40   $45.40  
  Purchase #7 $36.73   7.496%   $39.4833   $39.48   $39.50   $39.50  
  7 purchase totals = $555.10       $605.9833   $605.98   $605.90   $606.00