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 $51.77   11.443%   $57.694   $57.69   $57.70   $57.70  
  Purchase #2 $43.86   4.782%   $45.9574   $45.96   $45.95   $46.00  
  Purchase #3 $66.57   6.605%   $70.9669   $70.97   $70.95   $71.00  
  Purchase #4 $213.42   6.507%   $227.3072   $227.31   $227.30   $227.30  
  Purchase #5 $197.97   10.494%   $218.745   $218.75   $218.75   $218.70  
  Purchase #6 $137.96   9.503%   $151.0703   $151.07   $151.05   $151.10  
  Purchase #7 $58.57   9.830%   $64.3274   $64.33   $64.35   $64.30  
  7 purchase totals = $770.12       $836.0682   $836.08   $836.05   $836.10