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 $124.25   7.306%   $133.3277   $133.33   $133.35   $133.30  
  Purchase #2 $56.92   10.542%   $62.9205   $62.92   $62.90   $62.90  
  Purchase #3 $238.93   7.231%   $256.207   $256.21   $256.20   $256.20  
  Purchase #4 $15.95   10.592%   $17.6394   $17.64   $17.65   $17.60  
  Purchase #5 $159.29   5.377%   $167.855   $167.86   $167.85   $167.90  
  Purchase #6 $101.88   6.561%   $108.5643   $108.56   $108.55   $108.60  
  Purchase #7 $136.70   11.501%   $152.4219   $152.42   $152.40   $152.40  
  7 purchase totals = $833.92       $898.9358   $898.94   $898.90   $898.90