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 $244.66   12.691%   $275.7098   $275.71   $275.70   $275.70  
  Purchase #2 $155.98   7.476%   $167.6411   $167.64   $167.65   $167.60  
  Purchase #3 $135.47   4.144%   $141.0839   $141.08   $141.10   $141.10  
  Purchase #4 $231.46   13.152%   $261.9016   $261.90   $261.90   $261.90  
  Purchase #5 $209.57   11.487%   $233.6433   $233.64   $233.65   $233.60  
  Purchase #6 $110.81   5.507%   $116.9123   $116.91   $116.90   $116.90  
  Purchase #7 $79.25   8.631%   $86.0901   $86.09   $86.10   $86.10  
  7 purchase totals = $1,167.20       $1,282.9821   $1,282.97   $1,283.00   $1,282.90