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 $95.96   4.667%   $100.4385   $100.44   $100.45   $100.40  
  Purchase #2 $157.79   7.773%   $170.055   $170.06   $170.05   $170.10  
  Purchase #3 $16.82   3.817%   $17.462   $17.46   $17.45   $17.50  
  Purchase #4 $27.38   13.501%   $31.0766   $31.08   $31.10   $31.10  
  Purchase #5 $137.67   7.555%   $148.071   $148.07   $148.05   $148.10  
  Purchase #6 $157.81   11.352%   $175.7246   $175.72   $175.70   $175.70  
  Purchase #7 $158.77   6.544%   $169.1599   $169.16   $169.15   $169.20  
  7 purchase totals = $752.20       $811.9876   $811.99   $811.95   $812.10