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 $32.41   13.198%   $36.6875   $36.69   $36.70   $36.70  
  Purchase #2 $131.38   12.773%   $148.1612   $148.16   $148.15   $148.20  
  Purchase #3 $26.85   9.315%   $29.3511   $29.35   $29.35   $29.40  
  Purchase #4 $205.93   3.151%   $212.4189   $212.42   $212.40   $212.40  
  Purchase #5 $31.93   3.200%   $32.9518   $32.95   $32.95   $33.00  
  Purchase #6 $46.70   3.312%   $48.2467   $48.25   $48.25   $48.20  
  Purchase #7 $139.66   3.752%   $144.9   $144.90   $144.90   $144.90  
  7 purchase totals = $614.86       $652.7172   $652.72   $652.70   $652.80