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 $48.45   6.202%   $51.4549   $51.45   $51.45   $51.50  
  Purchase #2 $113.93   10.306%   $125.6716   $125.67   $125.65   $125.70  
  Purchase #3 $170.59   7.304%   $183.0499   $183.05   $183.05   $183.00  
  Purchase #4 $237.74   12.688%   $267.9045   $267.90   $267.90   $267.90  
  Purchase #5 $175.38   9.337%   $191.7552   $191.76   $191.75   $191.80  
  Purchase #6 $171.25   4.447%   $178.8655   $178.87   $178.85   $178.90  
  Purchase #7 $36.45   10.609%   $40.317   $40.32   $40.30   $40.30  
  7 purchase totals = $953.79       $1,039.0186   $1,039.02   $1,038.95   $1,039.10