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 $18.45   4.843%   $19.3435   $19.34   $19.35   $19.30  
  Purchase #2 $46.54   4.294%   $48.5384   $48.54   $48.55   $48.50  
  Purchase #3 $114.64   3.869%   $119.0754   $119.08   $119.10   $119.10  
  Purchase #4 $169.87   9.260%   $185.6   $185.60   $185.60   $185.60  
  Purchase #5 $173.47   11.218%   $192.9299   $192.93   $192.95   $192.90  
  Purchase #6 $236.90   11.636%   $264.4657   $264.47   $264.45   $264.50  
  Purchase #7 $121.93   11.787%   $136.3019   $136.30   $136.30   $136.30  
  7 purchase totals = $881.80       $966.2548   $966.26   $966.30   $966.20