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 $32.48   8.367%   $35.1976   $35.20   $35.20   $35.20  
  Purchase #2 $248.33   5.113%   $261.0271   $261.03   $261.05   $261.00  
  Purchase #3 $119.31   9.803%   $131.006   $131.01   $131.00   $131.00  
  Purchase #4 $18.67   4.825%   $19.5708   $19.57   $19.55   $19.60  
  Purchase #5 $104.87   6.456%   $111.6404   $111.64   $111.65   $111.60  
  Purchase #6 $241.82   4.336%   $252.3053   $252.31   $252.30   $252.30  
  Purchase #7 $71.58   3.161%   $73.8426   $73.84   $73.85   $73.80  
  7 purchase totals = $837.06       $884.5898   $884.60   $884.60   $884.50