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 $98.88   8.350%   $107.1365   $107.14   $107.15   $107.10  
  Purchase #2 $84.51   11.773%   $94.4594   $94.46   $94.45   $94.50  
  Purchase #3 $8.93   3.614%   $9.2527   $9.25   $9.25   $9.30  
  Purchase #4 $191.86   8.644%   $208.4444   $208.44   $208.45   $208.40  
  Purchase #5 $187.38   5.281%   $197.2755   $197.28   $197.30   $197.30  
  Purchase #6 $91.79   8.611%   $99.694   $99.69   $99.70   $99.70  
  Purchase #7 $204.77   12.394%   $230.1492   $230.15   $230.15   $230.10  
  7 purchase totals = $868.12       $946.4117   $946.41   $946.45   $946.40