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 $55.89   8.496%   $60.6384   $60.64   $60.65   $60.60  
  Purchase #2 $177.43   9.341%   $194.0037   $194.00   $194.00   $194.00  
  Purchase #3 $230.67   7.860%   $248.8007   $248.80   $248.80   $248.80  
  Purchase #4 $45.66   12.441%   $51.3406   $51.34   $51.35   $51.30  
  Purchase #5 $237.71   11.530%   $265.118   $265.12   $265.10   $265.10  
  Purchase #6 $185.82   3.784%   $192.8514   $192.85   $192.85   $192.90  
  Purchase #7 $152.59   11.170%   $169.6343   $169.63   $169.65   $169.60  
  7 purchase totals = $1,085.77       $1,182.3871   $1,182.38   $1,182.40   $1,182.30