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 $87.49   5.252%   $92.085   $92.09   $92.10   $92.10  
  Purchase #2 $47.47   4.179%   $49.4538   $49.45   $49.45   $49.50  
  Purchase #3 $69.62   6.576%   $74.1982   $74.20   $74.20   $74.20  
  Purchase #4 $13.50   4.691%   $14.1333   $14.13   $14.15   $14.10  
  Purchase #5 $64.26   7.291%   $68.9452   $68.95   $68.95   $68.90  
  Purchase #6 $121.40   4.335%   $126.6627   $126.66   $126.65   $126.70  
  Purchase #7 $101.47   4.252%   $105.7845   $105.78   $105.80   $105.80  
  7 purchase totals = $505.21       $531.2627   $531.26   $531.30   $531.30