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 $241.93   9.756%   $265.5327   $265.53   $265.55   $265.50  
  Purchase #2 $107.44   6.590%   $114.5203   $114.52   $114.50   $114.50  
  Purchase #3 $212.55   10.251%   $234.3385   $234.34   $234.35   $234.30  
  Purchase #4 $236.73   3.592%   $245.2333   $245.23   $245.25   $245.20  
  Purchase #5 $91.90   11.276%   $102.2626   $102.26   $102.25   $102.30  
  Purchase #6 $119.81   7.201%   $128.4375   $128.44   $128.45   $128.40  
  Purchase #7 $113.91   6.389%   $121.1877   $121.19   $121.20   $121.20  
  7 purchase totals = $1,124.27       $1,211.5126   $1,211.51   $1,211.55   $1,211.40