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 $159.68   4.730%   $167.2329   $167.23   $167.25   $167.20  
  Purchase #2 $211.84   8.707%   $230.2849   $230.28   $230.30   $230.30  
  Purchase #3 $217.89   4.522%   $227.743   $227.74   $227.75   $227.70  
  Purchase #4 $59.47   4.810%   $62.3305   $62.33   $62.35   $62.30  
  Purchase #5 $63.41   4.124%   $66.025   $66.03   $66.05   $66.00  
  Purchase #6 $68.75   7.718%   $74.0561   $74.06   $74.05   $74.10  
  Purchase #7 $128.65   3.676%   $133.3792   $133.38   $133.40   $133.40  
  7 purchase totals = $909.69       $961.0516   $961.05   $961.15   $961.00