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 $24.76   5.329%   $26.0795   $26.08   $26.10   $26.10  
  Purchase #2 $58.95   13.157%   $66.7061   $66.71   $66.70   $66.70  
  Purchase #3 $119.72   10.301%   $132.0524   $132.05   $132.05   $132.10  
  Purchase #4 $215.91   13.367%   $244.7707   $244.77   $244.75   $244.80  
  Purchase #5 $82.27   12.672%   $92.6953   $92.70   $92.70   $92.70  
  Purchase #6 $72.65   5.411%   $76.5811   $76.58   $76.60   $76.60  
  Purchase #7 $41.47   11.206%   $46.1171   $46.12   $46.10   $46.10  
  7 purchase totals = $615.73       $685.0022   $685.01   $685.00   $685.10