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 $56.51   8.371%   $61.2405   $61.24   $61.25   $61.20  
  Purchase #2 $233.91   9.521%   $256.1806   $256.18   $256.20   $256.20  
  Purchase #3 $57.71   12.362%   $64.8441   $64.84   $64.85   $64.80  
  Purchase #4 $58.29   6.374%   $62.0054   $62.01   $62.00   $62.00  
  Purchase #5 $182.98   6.552%   $194.9688   $194.97   $194.95   $195.00  
  Purchase #6 $167.42   10.695%   $185.3256   $185.33   $185.35   $185.30  
  Purchase #7 $153.75   6.601%   $163.899   $163.90   $163.90   $163.90  
  7 purchase totals = $910.57       $988.4640   $988.47   $988.50   $988.40