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 $41.78   13.267%   $47.323   $47.32   $47.30   $47.30  
  Purchase #2 $74.59   7.113%   $79.8956   $79.90   $79.90   $79.90  
  Purchase #3 $100.38   5.872%   $106.2743   $106.27   $106.25   $106.30  
  Purchase #4 $240.25   4.492%   $251.042   $251.04   $251.05   $251.00  
  Purchase #5 $208.71   11.766%   $233.2668   $233.27   $233.25   $233.30  
  Purchase #6 $206.66   8.146%   $223.4945   $223.49   $223.50   $223.50  
  Purchase #7 $11.73   8.848%   $12.7679   $12.77   $12.75   $12.80  
  7 purchase totals = $884.10       $954.0641   $954.06   $954.00   $954.10