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 $85.66   8.331%   $92.7963   $92.80   $92.80   $92.80  
  Purchase #2 $187.68   9.365%   $205.2562   $205.26   $205.25   $205.30  
  Purchase #3 $118.27   8.202%   $127.9705   $127.97   $127.95   $128.00  
  Purchase #4 $90.82   5.149%   $95.4963   $95.50   $95.50   $95.50  
  Purchase #5 $110.46   8.545%   $119.8988   $119.90   $119.90   $119.90  
  Purchase #6 $78.30   12.750%   $88.2833   $88.28   $88.30   $88.30  
  Purchase #7 $19.82   11.832%   $22.1651   $22.17   $22.15   $22.20  
  7 purchase totals = $691.01       $751.8665   $751.88   $751.85   $752.00