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 $184.65   11.722%   $206.2947   $206.29   $206.30   $206.30  
  Purchase #2 $49.54   9.581%   $54.2864   $54.29   $54.30   $54.30  
  Purchase #3 $156.65   13.177%   $177.2918   $177.29   $177.30   $177.30  
  Purchase #4 $245.26   13.519%   $278.4167   $278.42   $278.40   $278.40  
  Purchase #5 $108.82   6.844%   $116.2676   $116.27   $116.25   $116.30  
  Purchase #6 $243.28   11.498%   $271.2523   $271.25   $271.25   $271.30  
  Purchase #7 $107.78   5.789%   $114.0194   $114.02   $114.00   $114.00  
  7 purchase totals = $1,095.98       $1,217.8289   $1,217.83   $1,217.80   $1,217.90