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 $93.69   3.430%   $96.9036   $96.90   $96.90   $96.90  
  Purchase #2 $30.65   6.733%   $32.7137   $32.71   $32.70   $32.70  
  Purchase #3 $156.79   10.709%   $173.5806   $173.58   $173.60   $173.60  
  Purchase #4 $192.37   3.664%   $199.4184   $199.42   $199.40   $199.40  
  Purchase #5 $11.76   5.166%   $12.3675   $12.37   $12.35   $12.40  
  Purchase #6 $213.31   5.145%   $224.2848   $224.28   $224.30   $224.30  
  Purchase #7 $203.68   5.132%   $214.1329   $214.13   $214.15   $214.10  
  7 purchase totals = $902.25       $953.4015   $953.39   $953.40   $953.40