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 $185.44   4.632%   $194.0296   $194.03   $194.05   $194.00  
  Purchase #2 $106.67   11.729%   $119.1813   $119.18   $119.20   $119.20  
  Purchase #3 $235.41   8.490%   $255.3963   $255.40   $255.40   $255.40  
  Purchase #4 $135.53   8.399%   $146.9132   $146.91   $146.90   $146.90  
  Purchase #5 $140.94   3.346%   $145.6559   $145.66   $145.65   $145.70  
  Purchase #6 $228.81   7.838%   $246.7441   $246.74   $246.75   $246.70  
  Purchase #7 $217.39   10.541%   $240.3051   $240.31   $240.30   $240.30  
  7 purchase totals = $1,250.19       $1,348.2255   $1,348.23   $1,348.25   $1,348.20