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 $34.38   6.272%   $36.5363   $36.54   $36.55   $36.50  
  Purchase #2 $229.81   6.379%   $244.4696   $244.47   $244.45   $244.50  
  Purchase #3 $101.32   11.287%   $112.756   $112.76   $112.75   $112.80  
  Purchase #4 $62.77   8.790%   $68.2875   $68.29   $68.30   $68.30  
  Purchase #5 $119.38   12.735%   $134.583   $134.58   $134.60   $134.60  
  Purchase #6 $139.82   9.738%   $153.4357   $153.44   $153.45   $153.40  
  Purchase #7 $32.93   4.738%   $34.4902   $34.49   $34.50   $34.50  
  7 purchase totals = $720.41       $784.5583   $784.57   $784.60   $784.60