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 $201.80   8.361%   $218.6725   $218.67   $218.65   $218.70  
  Purchase #2 $91.62   8.729%   $99.6175   $99.62   $99.60   $99.60  
  Purchase #3 $59.74   5.858%   $63.2396   $63.24   $63.25   $63.20  
  Purchase #4 $17.64   11.583%   $19.6832   $19.68   $19.70   $19.70  
  Purchase #5 $233.80   11.353%   $260.3433   $260.34   $260.35   $260.30  
  Purchase #6 $57.49   7.325%   $61.7011   $61.70   $61.70   $61.70  
  Purchase #7 $42.53   12.711%   $47.936   $47.94   $47.95   $47.90  
  7 purchase totals = $704.62       $771.1932   $771.19   $771.20   $771.10