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 $112.25   10.669%   $124.226   $124.23   $124.25   $124.20  
  Purchase #2 $12.93   8.700%   $14.0549   $14.05   $14.05   $14.10  
  Purchase #3 $221.70   13.219%   $251.0065   $251.01   $251.00   $251.00  
  Purchase #4 $222.73   10.466%   $246.0409   $246.04   $246.05   $246.00  
  Purchase #5 $167.86   11.501%   $187.1656   $187.17   $187.15   $187.20  
  Purchase #6 $173.43   5.486%   $182.9444   $182.94   $182.95   $182.90  
  Purchase #7 $72.29   6.372%   $76.8963   $76.90   $76.90   $76.90  
  7 purchase totals = $983.19       $1,082.3346   $1,082.34   $1,082.35   $1,082.30