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 $34.66   11.290%   $38.5731   $38.57   $38.55   $38.60  
  Purchase #2 $53.42   4.602%   $55.8784   $55.88   $55.90   $55.90  
  Purchase #3 $86.87   7.313%   $93.2228   $93.22   $93.20   $93.20  
  Purchase #4 $109.33   8.515%   $118.6394   $118.64   $118.65   $118.60  
  Purchase #5 $212.63   13.357%   $241.031   $241.03   $241.05   $241.00  
  Purchase #6 $231.67   8.632%   $251.6678   $251.67   $251.65   $251.70  
  Purchase #7 $209.96   3.233%   $216.748   $216.75   $216.75   $216.70  
  7 purchase totals = $938.54       $1,015.7605   $1,015.76   $1,015.75   $1,015.70