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 $79.25   6.220%   $84.1794   $84.18   $84.20   $84.20  
  Purchase #2 $216.61   4.158%   $225.6166   $225.62   $225.60   $225.60  
  Purchase #3 $107.25   7.177%   $114.9473   $114.95   $114.95   $114.90  
  Purchase #4 $74.50   11.130%   $82.7919   $82.79   $82.80   $82.80  
  Purchase #5 $72.79   4.257%   $75.8887   $75.89   $75.90   $75.90  
  Purchase #6 $83.26   10.802%   $92.2537   $92.25   $92.25   $92.30  
  Purchase #7 $60.34   13.566%   $68.5257   $68.53   $68.55   $68.50  
  7 purchase totals = $694.00       $744.2033   $744.21   $744.25   $744.20