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 $32.47   13.802%   $36.9515   $36.95   $36.95   $37.00  
  Purchase #2 $228.98   11.628%   $255.6058   $255.61   $255.60   $255.60  
  Purchase #3 $244.42   10.704%   $270.5827   $270.58   $270.60   $270.60  
  Purchase #4 $113.51   11.549%   $126.6193   $126.62   $126.60   $126.60  
  Purchase #5 $12.87   13.244%   $14.5745   $14.57   $14.55   $14.60  
  Purchase #6 $218.78   8.238%   $236.8031   $236.80   $236.80   $236.80  
  Purchase #7 $23.32   12.606%   $26.2597   $26.26   $26.25   $26.30  
  7 purchase totals = $874.35       $967.3966   $967.39   $967.35   $967.50