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 $226.73   12.855%   $255.8761   $255.88   $255.90   $255.90  
  Purchase #2 $93.37   3.420%   $96.5633   $96.56   $96.55   $96.60  
  Purchase #3 $246.83   8.395%   $267.5514   $267.55   $267.55   $267.60  
  Purchase #4 $150.83   4.320%   $157.3459   $157.35   $157.35   $157.30  
  Purchase #5 $142.62   5.134%   $149.9421   $149.94   $149.95   $149.90  
  Purchase #6 $79.76   8.582%   $86.605   $86.61   $86.60   $86.60  
  Purchase #7 $224.31   11.628%   $250.3928   $250.39   $250.40   $250.40  
  7 purchase totals = $1,164.45       $1,264.2766   $1,264.28   $1,264.30   $1,264.30