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 $240.83   5.185%   $253.317   $253.32   $253.30   $253.30  
  Purchase #2 $114.93   3.176%   $118.5802   $118.58   $118.60   $118.60  
  Purchase #3 $8.79   4.874%   $9.2184   $9.22   $9.20   $9.20  
  Purchase #4 $156.89   6.735%   $167.4565   $167.46   $167.45   $167.50  
  Purchase #5 $240.33   6.268%   $255.3939   $255.39   $255.40   $255.40  
  Purchase #6 $156.82   8.214%   $169.7012   $169.70   $169.70   $169.70  
  Purchase #7 $67.41   9.457%   $73.785   $73.79   $73.80   $73.80  
  7 purchase totals = $986.00       $1,047.4522   $1,047.46   $1,047.45   $1,047.50