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 $56.62   7.639%   $60.9452   $60.95   $60.95   $60.90  
  Purchase #2 $157.49   10.696%   $174.3351   $174.34   $174.35   $174.30  
  Purchase #3 $162.39   3.689%   $168.3806   $168.38   $168.40   $168.40  
  Purchase #4 $206.73   10.698%   $228.846   $228.85   $228.85   $228.80  
  Purchase #5 $141.47   11.444%   $157.6598   $157.66   $157.65   $157.70  
  Purchase #6 $21.76   12.119%   $24.3971   $24.40   $24.40   $24.40  
  Purchase #7 $159.31   10.640%   $176.2606   $176.26   $176.25   $176.30  
  7 purchase totals = $905.77       $990.8244   $990.84   $990.85   $990.80