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 $232.74   8.171%   $251.7572   $251.76   $251.75   $251.80  
  Purchase #2 $232.40   9.402%   $254.2502   $254.25   $254.25   $254.30  
  Purchase #3 $67.80   12.366%   $76.1841   $76.18   $76.20   $76.20  
  Purchase #4 $67.79   12.444%   $76.2258   $76.23   $76.25   $76.20  
  Purchase #5 $34.73   5.420%   $36.6124   $36.61   $36.60   $36.60  
  Purchase #6 $108.90   6.258%   $115.715   $115.72   $115.70   $115.70  
  Purchase #7 $67.56   5.353%   $71.1765   $71.18   $71.20   $71.20  
  7 purchase totals = $811.92       $881.9212   $881.93   $881.95   $882.00