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 $66.98   3.662%   $69.4328   $69.43   $69.45   $69.40  
  Purchase #2 $90.97   12.733%   $102.5532   $102.55   $102.55   $102.60  
  Purchase #3 $11.90   13.430%   $13.4982   $13.50   $13.50   $13.50  
  Purchase #4 $157.87   10.565%   $174.549   $174.55   $174.55   $174.50  
  Purchase #5 $10.33   9.729%   $11.335   $11.34   $11.35   $11.30  
  Purchase #6 $192.74   11.565%   $215.0304   $215.03   $215.05   $215.00  
  Purchase #7 $137.96   7.444%   $148.2297   $148.23   $148.25   $148.20  
  7 purchase totals = $668.75       $734.6283   $734.63   $734.70   $734.50