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 $79.85   7.355%   $85.723   $85.72   $85.70   $85.70  
  Purchase #2 $91.90   5.869%   $97.2936   $97.29   $97.30   $97.30  
  Purchase #3 $61.37   4.792%   $64.3109   $64.31   $64.30   $64.30  
  Purchase #4 $183.25   3.313%   $189.3211   $189.32   $189.30   $189.30  
  Purchase #5 $115.75   12.547%   $130.2732   $130.27   $130.25   $130.30  
  Purchase #6 $190.99   4.636%   $199.8443   $199.84   $199.85   $199.80  
  Purchase #7 $105.80   3.298%   $109.2893   $109.29   $109.30   $109.30  
  7 purchase totals = $828.91       $876.0554   $876.04   $876.00   $876.00