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 $209.89   10.865%   $232.6945   $232.69   $232.70   $232.70  
  Purchase #2 $16.62   13.522%   $18.8674   $18.87   $18.85   $18.90  
  Purchase #3 $134.29   6.454%   $142.9571   $142.96   $142.95   $143.00  
  Purchase #4 $115.97   9.398%   $126.8689   $126.87   $126.85   $126.90  
  Purchase #5 $201.91   13.549%   $229.2668   $229.27   $229.25   $229.30  
  Purchase #6 $131.59   11.571%   $146.8163   $146.82   $146.80   $146.80  
  Purchase #7 $110.73   5.821%   $117.1756   $117.18   $117.20   $117.20  
  7 purchase totals = $921.00       $1,014.6466   $1,014.66   $1,014.60   $1,014.80