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 $158.37   5.605%   $167.2466   $167.25   $167.25   $167.20  
  Purchase #2 $79.31   6.693%   $84.6182   $84.62   $84.60   $84.60  
  Purchase #3 $228.30   7.244%   $244.8381   $244.84   $244.85   $244.80  
  Purchase #4 $85.41   3.746%   $88.6095   $88.61   $88.60   $88.60  
  Purchase #5 $231.49   7.561%   $248.993   $248.99   $249.00   $249.00  
  Purchase #6 $226.83   10.617%   $250.9125   $250.91   $250.90   $250.90  
  Purchase #7 $149.75   4.562%   $156.5816   $156.58   $156.60   $156.60  
  7 purchase totals = $1,159.46       $1,241.7995   $1,241.80   $1,241.80   $1,241.70