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 $25.86   3.782%   $26.838   $26.84   $26.85   $26.80  
  Purchase #2 $234.58   12.863%   $264.754   $264.75   $264.75   $264.80  
  Purchase #3 $85.78   13.646%   $97.4855   $97.49   $97.50   $97.50  
  Purchase #4 $159.82   6.392%   $170.0357   $170.04   $170.05   $170.00  
  Purchase #5 $105.53   12.767%   $119.003   $119.00   $119.00   $119.00  
  Purchase #6 $20.95   11.143%   $23.2845   $23.28   $23.30   $23.30  
  Purchase #7 $229.65   7.131%   $246.0263   $246.03   $246.05   $246.00  
  7 purchase totals = $862.17       $947.4270   $947.43   $947.50   $947.40