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 $31.43   12.763%   $35.4414   $35.44   $35.45   $35.40  
  Purchase #2 $233.85   9.437%   $255.9184   $255.92   $255.90   $255.90  
  Purchase #3 $149.69   11.356%   $166.6888   $166.69   $166.70   $166.70  
  Purchase #4 $132.37   13.102%   $149.7131   $149.71   $149.70   $149.70  
  Purchase #5 $234.72   7.601%   $252.5611   $252.56   $252.55   $252.60  
  Purchase #6 $192.48   9.641%   $211.037   $211.04   $211.05   $211.00  
  Purchase #7 $161.77   4.230%   $168.6129   $168.61   $168.60   $168.60  
  7 purchase totals = $1,136.31       $1,239.9727   $1,239.97   $1,239.95   $1,239.90