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 $173.91   11.378%   $193.6975   $193.70   $193.70   $193.70  
  Purchase #2 $120.78   9.228%   $131.9256   $131.93   $131.95   $131.90  
  Purchase #3 $249.45   7.451%   $268.0365   $268.04   $268.05   $268.00  
  Purchase #4 $67.82   11.859%   $75.8628   $75.86   $75.85   $75.90  
  Purchase #5 $134.53   9.159%   $146.8516   $146.85   $146.85   $146.90  
  Purchase #6 $6.50   5.872%   $6.8817   $6.88   $6.90   $6.90  
  Purchase #7 $54.85   8.722%   $59.634   $59.63   $59.65   $59.60  
  7 purchase totals = $807.84       $882.8897   $882.89   $882.95   $882.90