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 $206.97   13.851%   $235.6374   $235.64   $235.65   $235.60  
  Purchase #2 $103.80   7.373%   $111.4532   $111.45   $111.45   $111.50  
  Purchase #3 $88.36   7.492%   $94.9799   $94.98   $95.00   $95.00  
  Purchase #4 $108.33   5.411%   $114.1917   $114.19   $114.20   $114.20  
  Purchase #5 $195.46   10.583%   $216.1455   $216.15   $216.15   $216.10  
  Purchase #6 $162.81   13.526%   $184.8317   $184.83   $184.85   $184.80  
  Purchase #7 $236.53   7.776%   $254.9226   $254.92   $254.90   $254.90  
  7 purchase totals = $1,102.26       $1,212.1620   $1,212.16   $1,212.20   $1,212.10