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 $226.35   13.659%   $257.2671   $257.27   $257.25   $257.30  
  Purchase #2 $238.55   3.402%   $246.6655   $246.67   $246.65   $246.70  
  Purchase #3 $41.64   5.772%   $44.0435   $44.04   $44.05   $44.00  
  Purchase #4 $116.42   8.857%   $126.7313   $126.73   $126.75   $126.70  
  Purchase #5 $137.57   12.331%   $154.5338   $154.53   $154.55   $154.50  
  Purchase #6 $41.73   13.620%   $47.4136   $47.41   $47.40   $47.40  
  Purchase #7 $115.73   8.150%   $125.162   $125.16   $125.15   $125.20  
  7 purchase totals = $917.99       $1,001.8168   $1,001.81   $1,001.80   $1,001.80