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 $151.70   10.274%   $167.2857   $167.29   $167.30   $167.30  
  Purchase #2 $47.47   4.420%   $49.5682   $49.57   $49.55   $49.60  
  Purchase #3 $44.28   9.205%   $48.356   $48.36   $48.35   $48.40  
  Purchase #4 $199.89   7.173%   $214.2281   $214.23   $214.25   $214.20  
  Purchase #5 $59.98   4.526%   $62.6947   $62.69   $62.70   $62.70  
  Purchase #6 $85.39   11.295%   $95.0348   $95.03   $95.05   $95.00  
  Purchase #7 $219.37   7.757%   $236.3865   $236.39   $236.40   $236.40  
  7 purchase totals = $808.08       $873.5540   $873.56   $873.60   $873.60