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 $228.87   7.643%   $246.3625   $246.36   $246.35   $246.40  
  Purchase #2 $61.46   13.270%   $69.6157   $69.62   $69.60   $69.60  
  Purchase #3 $67.39   8.690%   $73.2462   $73.25   $73.25   $73.20  
  Purchase #4 $55.27   12.548%   $62.2053   $62.21   $62.20   $62.20  
  Purchase #5 $87.43   12.810%   $98.6298   $98.63   $98.65   $98.60  
  Purchase #6 $142.87   7.231%   $153.2009   $153.20   $153.20   $153.20  
  Purchase #7 $108.46   4.552%   $113.3971   $113.40   $113.40   $113.40  
  7 purchase totals = $751.75       $816.6575   $816.67   $816.65   $816.60