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 $239.66   11.387%   $266.9501   $266.95   $266.95   $267.00  
  Purchase #2 $116.58   7.493%   $125.3153   $125.32   $125.30   $125.30  
  Purchase #3 $169.38   10.782%   $187.6426   $187.64   $187.65   $187.60  
  Purchase #4 $141.82   6.855%   $151.5418   $151.54   $151.55   $151.50  
  Purchase #5 $21.42   8.150%   $23.1657   $23.17   $23.15   $23.20  
  Purchase #6 $166.28   13.762%   $189.1635   $189.16   $189.15   $189.20  
  Purchase #7 $48.79   12.281%   $54.7819   $54.78   $54.80   $54.80  
  7 purchase totals = $903.93       $998.5609   $998.56   $998.55   $998.60