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 $113.92   11.103%   $126.5685   $126.57   $126.55   $126.60  
  Purchase #2 $192.39   3.665%   $199.4411   $199.44   $199.45   $199.40  
  Purchase #3 $194.64   8.306%   $210.8068   $210.81   $210.80   $210.80  
  Purchase #4 $66.65   10.772%   $73.8295   $73.83   $73.85   $73.80  
  Purchase #5 $50.84   6.284%   $54.0348   $54.03   $54.05   $54.00  
  Purchase #6 $248.28   3.749%   $257.588   $257.59   $257.60   $257.60  
  Purchase #7 $122.39   11.862%   $136.9079   $136.91   $136.90   $136.90  
  7 purchase totals = $989.11       $1,059.1766   $1,059.18   $1,059.20   $1,059.10