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 $234.39   6.628%   $249.9254   $249.93   $249.95   $249.90  
  Purchase #2 $157.87   3.633%   $163.6054   $163.61   $163.60   $163.60  
  Purchase #3 $127.29   11.304%   $141.6789   $141.68   $141.70   $141.70  
  Purchase #4 $110.73   4.764%   $116.0052   $116.01   $116.00   $116.00  
  Purchase #5 $162.63   4.121%   $169.332   $169.33   $169.35   $169.30  
  Purchase #6 $212.44   3.640%   $220.1728   $220.17   $220.15   $220.20  
  Purchase #7 $151.98   10.391%   $167.7722   $167.77   $167.75   $167.80  
  7 purchase totals = $1,157.33       $1,228.4919   $1,228.50   $1,228.50   $1,228.50