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 $182.62   13.547%   $207.3595   $207.36   $207.35   $207.40  
  Purchase #2 $11.39   13.293%   $12.9041   $12.90   $12.90   $12.90  
  Purchase #3 $197.62   8.369%   $214.1588   $214.16   $214.15   $214.20  
  Purchase #4 $91.68   4.288%   $95.6112   $95.61   $95.60   $95.60  
  Purchase #5 $111.40   12.806%   $125.6659   $125.67   $125.65   $125.70  
  Purchase #6 $240.38   4.370%   $250.8846   $250.88   $250.90   $250.90  
  Purchase #7 $155.36   7.868%   $167.5837   $167.58   $167.60   $167.60  
  7 purchase totals = $990.45       $1,074.1678   $1,074.16   $1,074.15   $1,074.30