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 $63.98   11.605%   $71.4049   $71.40   $71.40   $71.40  
  Purchase #2 $96.39   5.656%   $101.8418   $101.84   $101.85   $101.80  
  Purchase #3 $17.64   6.509%   $18.7882   $18.79   $18.80   $18.80  
  Purchase #4 $47.69   11.659%   $53.2502   $53.25   $53.25   $53.30  
  Purchase #5 $166.48   12.573%   $187.4115   $187.41   $187.40   $187.40  
  Purchase #6 $178.28   12.110%   $199.8697   $199.87   $199.85   $199.90  
  Purchase #7 $156.51   5.641%   $165.3387   $165.34   $165.35   $165.30  
  7 purchase totals = $726.97       $797.9050   $797.90   $797.90   $797.90