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 $86.67   10.785%   $96.0174   $96.02   $96.00   $96.00  
  Purchase #2 $43.58   8.707%   $47.3745   $47.37   $47.35   $47.40  
  Purchase #3 $116.88   9.236%   $127.675   $127.68   $127.70   $127.70  
  Purchase #4 $95.54   5.320%   $100.6227   $100.62   $100.60   $100.60  
  Purchase #5 $97.69   3.652%   $101.2576   $101.26   $101.25   $101.30  
  Purchase #6 $204.53   9.537%   $224.036   $224.04   $224.05   $224.00  
  Purchase #7 $82.50   7.544%   $88.7238   $88.72   $88.70   $88.70  
  7 purchase totals = $727.39       $785.7070   $785.71   $785.65   $785.70