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 $54.26   11.126%   $60.297   $60.30   $60.30   $60.30  
  Purchase #2 $16.40   8.427%   $17.782   $17.78   $17.80   $17.80  
  Purchase #3 $223.66   11.482%   $249.3406   $249.34   $249.35   $249.30  
  Purchase #4 $114.31   10.147%   $125.909   $125.91   $125.90   $125.90  
  Purchase #5 $201.49   5.589%   $212.7513   $212.75   $212.75   $212.80  
  Purchase #6 $109.79   4.538%   $114.7723   $114.77   $114.75   $114.80  
  Purchase #7 $157.95   10.196%   $174.0546   $174.05   $174.05   $174.10  
  7 purchase totals = $877.86       $954.9068   $954.90   $954.90   $955.00