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 $75.58   5.252%   $79.5495   $79.55   $79.55   $79.50  
  Purchase #2 $183.79   6.222%   $195.2254   $195.23   $195.25   $195.20  
  Purchase #3 $241.79   6.202%   $256.7858   $256.79   $256.80   $256.80  
  Purchase #4 $208.77   9.607%   $228.8265   $228.83   $228.85   $228.80  
  Purchase #5 $164.30   5.858%   $173.9247   $173.92   $173.90   $173.90  
  Purchase #6 $161.73   10.389%   $178.5321   $178.53   $178.55   $178.50  
  Purchase #7 $10.36   10.160%   $11.4126   $11.41   $11.40   $11.40  
  7 purchase totals = $1,046.32       $1,124.2566   $1,124.26   $1,124.30   $1,124.10