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 $42.71   4.413%   $44.5948   $44.59   $44.60   $44.60  
  Purchase #2 $203.47   9.652%   $223.1089   $223.11   $223.10   $223.10  
  Purchase #3 $245.68   7.446%   $263.9733   $263.97   $263.95   $264.00  
  Purchase #4 $192.26   12.729%   $216.7328   $216.73   $216.75   $216.70  
  Purchase #5 $124.69   9.565%   $136.6166   $136.62   $136.60   $136.60  
  Purchase #6 $14.28   9.428%   $15.6263   $15.63   $15.65   $15.60  
  Purchase #7 $241.59   4.692%   $252.9254   $252.93   $252.95   $252.90  
  7 purchase totals = $1,064.68       $1,153.5781   $1,153.58   $1,153.60   $1,153.50