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 $73.45   3.489%   $76.0127   $76.01   $76.00   $76.00  
  Purchase #2 $70.43   8.282%   $76.263   $76.26   $76.25   $76.30  
  Purchase #3 $16.95   10.760%   $18.7738   $18.77   $18.75   $18.80  
  Purchase #4 $246.90   11.606%   $275.5552   $275.56   $275.55   $275.60  
  Purchase #5 $105.86   8.115%   $114.4505   $114.45   $114.45   $114.50  
  Purchase #6 $160.87   8.254%   $174.1482   $174.15   $174.15   $174.10  
  Purchase #7 $36.34   3.496%   $37.6104   $37.61   $37.60   $37.60  
  7 purchase totals = $710.80       $772.8138   $772.81   $772.75   $772.90