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 $114.77   10.548%   $126.8759   $126.88   $126.90   $126.90  
  Purchase #2 $188.60   8.844%   $205.2798   $205.28   $205.30   $205.30  
  Purchase #3 $248.32   13.479%   $281.7911   $281.79   $281.80   $281.80  
  Purchase #4 $25.84   12.166%   $28.9837   $28.98   $29.00   $29.00  
  Purchase #5 $239.86   9.827%   $263.431   $263.43   $263.45   $263.40  
  Purchase #6 $167.91   13.749%   $190.9959   $191.00   $191.00   $191.00  
  Purchase #7 $6.26   11.860%   $7.0024   $7.00   $7.00   $7.00  
  7 purchase totals = $991.56       $1,104.3598   $1,104.36   $1,104.45   $1,104.40