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 $246.87   7.225%   $264.7064   $264.71   $264.70   $264.70  
  Purchase #2 $58.85   6.676%   $62.7788   $62.78   $62.80   $62.80  
  Purchase #3 $11.41   10.507%   $12.6088   $12.61   $12.60   $12.60  
  Purchase #4 $34.54   4.697%   $36.1623   $36.16   $36.15   $36.20  
  Purchase #5 $219.74   11.511%   $245.0343   $245.03   $245.05   $245.00  
  Purchase #6 $29.25   4.553%   $30.5818   $30.58   $30.60   $30.60  
  Purchase #7 $90.73   5.760%   $95.956   $95.96   $95.95   $96.00  
  7 purchase totals = $691.39       $747.8284   $747.83   $747.85   $747.90