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 $208.81   10.689%   $231.1297   $231.13   $231.15   $231.10  
  Purchase #2 $38.61   12.397%   $43.3965   $43.40   $43.40   $43.40  
  Purchase #3 $114.76   6.803%   $122.5671   $122.57   $122.55   $122.60  
  Purchase #4 $128.73   5.393%   $135.6724   $135.67   $135.65   $135.70  
  Purchase #5 $55.29   10.157%   $60.9058   $60.91   $60.90   $60.90  
  Purchase #6 $206.73   4.775%   $216.6014   $216.60   $216.60   $216.60  
  Purchase #7 $238.43   7.194%   $255.5827   $255.58   $255.60   $255.60  
  7 purchase totals = $991.36       $1,065.8556   $1,065.86   $1,065.85   $1,065.90