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 $48.88   11.754%   $54.6254   $54.63   $54.65   $54.60  
  Purchase #2 $151.34   8.817%   $164.6836   $164.68   $164.70   $164.70  
  Purchase #3 $163.40   7.282%   $175.2988   $175.30   $175.30   $175.30  
  Purchase #4 $190.38   4.727%   $199.3793   $199.38   $199.40   $199.40  
  Purchase #5 $86.55   3.284%   $89.3923   $89.39   $89.40   $89.40  
  Purchase #6 $59.87   3.125%   $61.7409   $61.74   $61.75   $61.70  
  Purchase #7 $65.50   11.672%   $73.1452   $73.15   $73.15   $73.10  
  7 purchase totals = $765.92       $818.2655   $818.27   $818.35   $818.20