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 $207.76   10.577%   $229.7348   $229.73   $229.75   $229.70  
  Purchase #2 $168.86   9.872%   $185.5299   $185.53   $185.55   $185.50  
  Purchase #3 $226.77   13.401%   $257.1594   $257.16   $257.15   $257.20  
  Purchase #4 $103.95   5.740%   $109.9167   $109.92   $109.90   $109.90  
  Purchase #5 $233.74   9.839%   $256.7377   $256.74   $256.75   $256.70  
  Purchase #6 $41.56   6.523%   $44.271   $44.27   $44.25   $44.30  
  Purchase #7 $152.38   10.230%   $167.9685   $167.97   $167.95   $168.00  
  7 purchase totals = $1,135.02       $1,251.3180   $1,251.32   $1,251.30   $1,251.30