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 $43.69   12.131%   $48.99   $48.99   $49.00   $49.00  
  Purchase #2 $151.65   10.846%   $168.098   $168.10   $168.10   $168.10  
  Purchase #3 $41.95   4.629%   $43.8919   $43.89   $43.90   $43.90  
  Purchase #4 $95.80   12.867%   $108.1266   $108.13   $108.15   $108.10  
  Purchase #5 $232.47   13.807%   $264.5671   $264.57   $264.55   $264.60  
  Purchase #6 $42.63   11.174%   $47.3935   $47.39   $47.40   $47.40  
  Purchase #7 $157.71   4.561%   $164.9032   $164.90   $164.90   $164.90  
  7 purchase totals = $765.90       $845.9703   $845.97   $846.00   $846.00