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 $174.70   5.456%   $184.2316   $184.23   $184.25   $184.20  
  Purchase #2 $10.79   4.719%   $11.2992   $11.30   $11.30   $11.30  
  Purchase #3 $159.60   10.610%   $176.5336   $176.53   $176.55   $176.50  
  Purchase #4 $214.73   12.523%   $241.6206   $241.62   $241.60   $241.60  
  Purchase #5 $123.47   9.628%   $135.3577   $135.36   $135.35   $135.40  
  Purchase #6 $233.73   3.746%   $242.4855   $242.49   $242.50   $242.50  
  Purchase #7 $219.73   13.846%   $250.1538   $250.15   $250.15   $250.20  
  7 purchase totals = $1,136.75       $1,241.6820   $1,241.68   $1,241.70   $1,241.70