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 $69.94   9.325%   $76.4619   $76.46   $76.45   $76.50  
  Purchase #2 $73.56   5.175%   $77.3667   $77.37   $77.35   $77.40  
  Purchase #3 $91.55   8.567%   $99.3931   $99.39   $99.40   $99.40  
  Purchase #4 $183.70   5.617%   $194.0184   $194.02   $194.00   $194.00  
  Purchase #5 $106.30   10.102%   $117.0384   $117.04   $117.05   $117.00  
  Purchase #6 $241.53   13.324%   $273.7115   $273.71   $273.70   $273.70  
  Purchase #7 $55.96   7.579%   $60.2012   $60.20   $60.20   $60.20  
  7 purchase totals = $822.54       $898.1912   $898.19   $898.15   $898.20