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 $59.38   11.703%   $66.3292   $66.33   $66.35   $66.30  
  Purchase #2 $31.51   7.578%   $33.8978   $33.90   $33.90   $33.90  
  Purchase #3 $137.47   8.321%   $148.9089   $148.91   $148.90   $148.90  
  Purchase #4 $96.36   11.805%   $107.7353   $107.74   $107.75   $107.70  
  Purchase #5 $86.98   6.195%   $92.3684   $92.37   $92.35   $92.40  
  Purchase #6 $208.55   12.770%   $235.1818   $235.18   $235.20   $235.20  
  Purchase #7 $128.54   8.391%   $139.3258   $139.33   $139.35   $139.30  
  7 purchase totals = $748.79       $823.7472   $823.76   $823.80   $823.70