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 $81.55   8.408%   $88.4067   $88.41   $88.40   $88.40  
  Purchase #2 $151.36   4.787%   $158.6056   $158.61   $158.60   $158.60  
  Purchase #3 $130.94   3.723%   $135.8149   $135.81   $135.80   $135.80  
  Purchase #4 $53.48   13.735%   $60.8255   $60.83   $60.85   $60.80  
  Purchase #5 $218.39   11.856%   $244.2823   $244.28   $244.30   $244.30  
  Purchase #6 $168.38   10.227%   $185.6002   $185.60   $185.60   $185.60  
  Purchase #7 $223.63   3.598%   $231.6762   $231.68   $231.70   $231.70  
  7 purchase totals = $1,027.73       $1,105.2114   $1,105.22   $1,105.25   $1,105.20