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 $35.73   10.630%   $39.5281   $39.53   $39.55   $39.50  
  Purchase #2 $241.67   5.824%   $255.7449   $255.74   $255.75   $255.70  
  Purchase #3 $69.34   6.117%   $73.5815   $73.58   $73.60   $73.60  
  Purchase #4 $228.26   5.512%   $240.8417   $240.84   $240.85   $240.80  
  Purchase #5 $107.67   4.237%   $112.232   $112.23   $112.25   $112.20  
  Purchase #6 $244.76   3.336%   $252.9252   $252.93   $252.95   $252.90  
  Purchase #7 $37.85   5.113%   $39.7853   $39.79   $39.80   $39.80  
  7 purchase totals = $965.28       $1,014.6387   $1,014.64   $1,014.75   $1,014.50