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 $247.57   5.673%   $261.6146   $261.61   $261.60   $261.60  
  Purchase #2 $175.52   6.323%   $186.6181   $186.62   $186.60   $186.60  
  Purchase #3 $23.71   13.836%   $26.9905   $26.99   $27.00   $27.00  
  Purchase #4 $16.47   3.790%   $17.0942   $17.09   $17.10   $17.10  
  Purchase #5 $190.59   9.812%   $209.2907   $209.29   $209.30   $209.30  
  Purchase #6 $105.91   10.726%   $117.2699   $117.27   $117.25   $117.30  
  Purchase #7 $204.91   5.299%   $215.7682   $215.77   $215.75   $215.80  
  7 purchase totals = $964.68       $1,034.6462   $1,034.64   $1,034.60   $1,034.70