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 $194.51   5.858%   $205.9044   $205.90   $205.90   $205.90  
  Purchase #2 $231.92   4.495%   $242.3448   $242.34   $242.35   $242.30  
  Purchase #3 $123.33   7.828%   $132.9843   $132.98   $133.00   $133.00  
  Purchase #4 $36.91   9.228%   $40.3161   $40.32   $40.30   $40.30  
  Purchase #5 $60.50   6.189%   $64.2443   $64.24   $64.25   $64.20  
  Purchase #6 $178.79   5.106%   $187.919   $187.92   $187.90   $187.90  
  Purchase #7 $96.86   12.562%   $109.0276   $109.03   $109.05   $109.00  
  7 purchase totals = $922.82       $982.7405   $982.73   $982.75   $982.60