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 $71.97   5.225%   $75.7304   $75.73   $75.75   $75.70  
  Purchase #2 $78.37   5.386%   $82.591   $82.59   $82.60   $82.60  
  Purchase #3 $99.95   6.536%   $106.4827   $106.48   $106.50   $106.50  
  Purchase #4 $179.75   11.515%   $200.4482   $200.45   $200.45   $200.40  
  Purchase #5 $7.80   3.120%   $8.0434   $8.04   $8.05   $8.00  
  Purchase #6 $179.26   7.144%   $192.0663   $192.07   $192.05   $192.10  
  Purchase #7 $47.25   8.661%   $51.3423   $51.34   $51.35   $51.30  
  7 purchase totals = $664.35       $716.7043   $716.70   $716.75   $716.60