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 $217.36   13.270%   $246.2037   $246.20   $246.20   $246.20  
  Purchase #2 $110.90   8.190%   $119.9827   $119.98   $120.00   $120.00  
  Purchase #3 $158.91   8.870%   $173.0053   $173.01   $173.00   $173.00  
  Purchase #4 $49.39   12.796%   $55.7099   $55.71   $55.70   $55.70  
  Purchase #5 $87.92   5.790%   $93.0106   $93.01   $93.00   $93.00  
  Purchase #6 $102.69   4.683%   $107.499   $107.50   $107.50   $107.50  
  Purchase #7 $104.85   3.243%   $108.2503   $108.25   $108.25   $108.30  
  7 purchase totals = $832.02       $903.6615   $903.66   $903.65   $903.70