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 $86.76   12.337%   $97.4636   $97.46   $97.45   $97.50  
  Purchase #2 $215.76   9.707%   $236.7038   $236.70   $236.70   $236.70  
  Purchase #3 $85.33   12.828%   $96.2761   $96.28   $96.30   $96.30  
  Purchase #4 $98.43   9.686%   $107.9639   $107.96   $107.95   $108.00  
  Purchase #5 $167.84   4.518%   $175.423   $175.42   $175.40   $175.40  
  Purchase #6 $89.94   5.858%   $95.2087   $95.21   $95.20   $95.20  
  Purchase #7 $23.38   6.358%   $24.8665   $24.87   $24.85   $24.90  
  7 purchase totals = $767.44       $833.9056   $833.90   $833.85   $834.00