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 $201.97   12.204%   $226.6184   $226.62   $226.60   $226.60  
  Purchase #2 $161.36   9.706%   $177.0216   $177.02   $177.00   $177.00  
  Purchase #3 $17.53   8.779%   $19.069   $19.07   $19.05   $19.10  
  Purchase #4 $67.74   5.231%   $71.2835   $71.28   $71.30   $71.30  
  Purchase #5 $163.95   13.492%   $186.0701   $186.07   $186.05   $186.10  
  Purchase #6 $151.84   6.575%   $161.8235   $161.82   $161.80   $161.80  
  Purchase #7 $39.85   5.489%   $42.0374   $42.04   $42.05   $42.00  
  7 purchase totals = $804.24       $883.9235   $883.92   $883.85   $883.90