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 $82.83   13.657%   $94.1421   $94.14   $94.15   $94.10  
  Purchase #2 $189.97   3.115%   $195.8876   $195.89   $195.90   $195.90  
  Purchase #3 $95.45   9.247%   $104.2763   $104.28   $104.30   $104.30  
  Purchase #4 $66.34   7.249%   $71.149   $71.15   $71.15   $71.10  
  Purchase #5 $190.64   9.778%   $209.2808   $209.28   $209.30   $209.30  
  Purchase #6 $199.37   13.658%   $226.6   $226.60   $226.60   $226.60  
  Purchase #7 $120.81   12.605%   $136.0381   $136.04   $136.05   $136.00  
  7 purchase totals = $945.41       $1,037.3739   $1,037.38   $1,037.45   $1,037.30