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 $26.99   4.424%   $28.184   $28.18   $28.20   $28.20  
  Purchase #2 $207.41   12.854%   $234.0705   $234.07   $234.05   $234.10  
  Purchase #3 $102.41   6.836%   $109.4107   $109.41   $109.40   $109.40  
  Purchase #4 $169.28   11.865%   $189.3651   $189.37   $189.35   $189.40  
  Purchase #5 $25.84   10.729%   $28.6124   $28.61   $28.60   $28.60  
  Purchase #6 $78.64   5.768%   $83.176   $83.18   $83.20   $83.20  
  Purchase #7 $233.76   12.117%   $262.0847   $262.08   $262.10   $262.10  
  7 purchase totals = $844.33       $934.9034   $934.90   $934.90   $935.00