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 $195.62   4.403%   $204.2331   $204.23   $204.25   $204.20  
  Purchase #2 $241.83   11.317%   $269.1979   $269.20   $269.20   $269.20  
  Purchase #3 $55.77   12.316%   $62.6386   $62.64   $62.65   $62.60  
  Purchase #4 $73.28   12.636%   $82.5397   $82.54   $82.55   $82.50  
  Purchase #5 $220.48   7.443%   $236.8903   $236.89   $236.90   $236.90  
  Purchase #6 $174.80   11.126%   $194.2482   $194.25   $194.25   $194.20  
  Purchase #7 $235.27   11.276%   $261.799   $261.80   $261.80   $261.80  
  7 purchase totals = $1,197.05       $1,311.5468   $1,311.55   $1,311.60   $1,311.40