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 $90.51   11.612%   $101.02   $101.02   $101.00   $101.00  
  Purchase #2 $117.48   10.863%   $130.2419   $130.24   $130.25   $130.20  
  Purchase #3 $57.93   8.785%   $63.0192   $63.02   $63.00   $63.00  
  Purchase #4 $151.47   10.469%   $167.3274   $167.33   $167.35   $167.30  
  Purchase #5 $243.63   13.802%   $277.2558   $277.26   $277.25   $277.30  
  Purchase #6 $155.86   4.189%   $162.389   $162.39   $162.40   $162.40  
  Purchase #7 $62.33   9.251%   $68.0961   $68.10   $68.10   $68.10  
  7 purchase totals = $879.21       $969.3494   $969.36   $969.35   $969.30