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 $150.44   11.647%   $167.9617   $167.96   $167.95   $168.00  
  Purchase #2 $215.72   5.650%   $227.9082   $227.91   $227.90   $227.90  
  Purchase #3 $113.29   3.183%   $116.896   $116.90   $116.90   $116.90  
  Purchase #4 $195.98   6.174%   $208.0798   $208.08   $208.10   $208.10  
  Purchase #5 $146.83   4.425%   $153.3272   $153.33   $153.35   $153.30  
  Purchase #6 $246.86   3.836%   $256.3295   $256.33   $256.35   $256.30  
  Purchase #7 $41.64   11.390%   $46.3828   $46.38   $46.40   $46.40  
  7 purchase totals = $1,110.76       $1,176.8852   $1,176.89   $1,176.95   $1,176.90