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 $48.44   9.514%   $53.0486   $53.05   $53.05   $53.00  
  Purchase #2 $225.68   11.404%   $251.4165   $251.42   $251.40   $251.40  
  Purchase #3 $175.89   11.256%   $195.6882   $195.69   $195.70   $195.70  
  Purchase #4 $26.90   3.667%   $27.8864   $27.89   $27.90   $27.90  
  Purchase #5 $32.53   10.799%   $36.0429   $36.04   $36.05   $36.00  
  Purchase #6 $233.82   5.819%   $247.426   $247.43   $247.45   $247.40  
  Purchase #7 $187.38   12.127%   $210.1036   $210.10   $210.10   $210.10  
  7 purchase totals = $930.64       $1,021.6122   $1,021.62   $1,021.65   $1,021.50