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 $60.97   9.448%   $66.7304   $66.73   $66.75   $66.70  
  Purchase #2 $10.44   6.859%   $11.1561   $11.16   $11.15   $11.20  
  Purchase #3 $78.59   9.226%   $85.8407   $85.84   $85.85   $85.80  
  Purchase #4 $169.54   7.593%   $182.4132   $182.41   $182.40   $182.40  
  Purchase #5 $235.86   3.738%   $244.6764   $244.68   $244.70   $244.70  
  Purchase #6 $161.66   7.415%   $173.6471   $173.65   $173.65   $173.60  
  Purchase #7 $59.80   7.307%   $64.1696   $64.17   $64.15   $64.20  
  7 purchase totals = $776.86       $828.6335   $828.64   $828.65   $828.60