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 $182.98   11.767%   $204.5113   $204.51   $204.50   $204.50  
  Purchase #2 $87.70   12.498%   $98.6607   $98.66   $98.65   $98.70  
  Purchase #3 $196.52   8.756%   $213.7273   $213.73   $213.75   $213.70  
  Purchase #4 $222.94   10.290%   $245.8805   $245.88   $245.90   $245.90  
  Purchase #5 $13.49   5.741%   $14.2645   $14.26   $14.25   $14.30  
  Purchase #6 $68.29   7.321%   $73.2895   $73.29   $73.30   $73.30  
  Purchase #7 $56.47   7.811%   $60.8809   $60.88   $60.90   $60.90  
  7 purchase totals = $828.39       $911.2147   $911.21   $911.25   $911.30