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 $69.27   8.124%   $74.8975   $74.90   $74.90   $74.90  
  Purchase #2 $137.88   5.689%   $145.724   $145.72   $145.70   $145.70  
  Purchase #3 $48.47   5.593%   $51.1809   $51.18   $51.20   $51.20  
  Purchase #4 $192.64   4.653%   $201.6035   $201.60   $201.60   $201.60  
  Purchase #5 $6.53   5.266%   $6.8739   $6.87   $6.85   $6.90  
  Purchase #6 $182.71   11.798%   $204.2661   $204.27   $204.25   $204.30  
  Purchase #7 $227.83   9.592%   $249.6835   $249.68   $249.70   $249.70  
  7 purchase totals = $865.33       $934.2294   $934.22   $934.20   $934.30