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 $106.47   7.829%   $114.8055   $114.81   $114.80   $114.80  
  Purchase #2 $237.90   13.412%   $269.8071   $269.81   $269.80   $269.80  
  Purchase #3 $202.43   3.337%   $209.1851   $209.19   $209.20   $209.20  
  Purchase #4 $67.63   3.376%   $69.9132   $69.91   $69.90   $69.90  
  Purchase #5 $238.54   3.467%   $246.8102   $246.81   $246.80   $246.80  
  Purchase #6 $137.75   10.299%   $151.9369   $151.94   $151.95   $151.90  
  Purchase #7 $162.64   5.818%   $172.1024   $172.10   $172.10   $172.10  
  7 purchase totals = $1,153.36       $1,234.5604   $1,234.57   $1,234.55   $1,234.50