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 $89.94   3.366%   $92.9674   $92.97   $92.95   $93.00  
  Purchase #2 $139.86   11.467%   $155.8977   $155.90   $155.90   $155.90  
  Purchase #3 $67.66   12.497%   $76.1155   $76.12   $76.10   $76.10  
  Purchase #4 $167.99   10.197%   $185.1199   $185.12   $185.10   $185.10  
  Purchase #5 $166.54   4.836%   $174.5939   $174.59   $174.60   $174.60  
  Purchase #6 $209.79   7.234%   $224.9662   $224.97   $224.95   $225.00  
  Purchase #7 $84.48   10.602%   $93.4366   $93.44   $93.45   $93.40  
  7 purchase totals = $926.26       $1,003.0972   $1,003.11   $1,003.05   $1,003.10