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 $70.25   6.804%   $75.0298   $75.03   $75.05   $75.00  
  Purchase #2 $167.72   4.747%   $175.6817   $175.68   $175.70   $175.70  
  Purchase #3 $247.85   13.230%   $280.6406   $280.64   $280.65   $280.60  
  Purchase #4 $194.28   10.200%   $214.0966   $214.10   $214.10   $214.10  
  Purchase #5 $192.38   10.849%   $213.2513   $213.25   $213.25   $213.30  
  Purchase #6 $201.27   11.251%   $223.9149   $223.91   $223.90   $223.90  
  Purchase #7 $114.29   4.776%   $119.7485   $119.75   $119.75   $119.70  
  7 purchase totals = $1,188.04       $1,302.3634   $1,302.36   $1,302.40   $1,302.30