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 $92.64   13.362%   $105.0186   $105.02   $105.00   $105.00  
  Purchase #2 $107.35   9.375%   $117.4141   $117.41   $117.40   $117.40  
  Purchase #3 $94.80   7.461%   $101.873   $101.87   $101.85   $101.90  
  Purchase #4 $25.74   10.664%   $28.4849   $28.48   $28.50   $28.50  
  Purchase #5 $110.34   3.597%   $114.3089   $114.31   $114.30   $114.30  
  Purchase #6 $197.42   9.139%   $215.4622   $215.46   $215.45   $215.50  
  Purchase #7 $155.92   10.466%   $172.2386   $172.24   $172.25   $172.20  
  7 purchase totals = $784.21       $854.8003   $854.79   $854.75   $854.80