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 $120.44   5.110%   $126.5945   $126.59   $126.60   $126.60  
  Purchase #2 $13.26   8.379%   $14.3711   $14.37   $14.35   $14.40  
  Purchase #3 $218.63   13.841%   $248.8906   $248.89   $248.90   $248.90  
  Purchase #4 $118.96   6.599%   $126.8102   $126.81   $126.80   $126.80  
  Purchase #5 $155.45   3.541%   $160.9545   $160.95   $160.95   $161.00  
  Purchase #6 $107.28   10.581%   $118.6313   $118.63   $118.65   $118.60  
  Purchase #7 $217.38   8.793%   $236.4942   $236.49   $236.50   $236.50  
  7 purchase totals = $951.40       $1,032.7464   $1,032.73   $1,032.75   $1,032.80