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 $56.96   11.569%   $63.5497   $63.55   $63.55   $63.50  
  Purchase #2 $234.42   11.814%   $262.1144   $262.11   $262.10   $262.10  
  Purchase #3 $172.81   8.863%   $188.1262   $188.13   $188.15   $188.10  
  Purchase #4 $157.48   5.802%   $166.617   $166.62   $166.60   $166.60  
  Purchase #5 $231.39   6.212%   $245.7639   $245.76   $245.75   $245.80  
  Purchase #6 $111.67   5.670%   $118.0017   $118.00   $118.00   $118.00  
  Purchase #7 $180.81   8.678%   $196.5007   $196.50   $196.50   $196.50  
  7 purchase totals = $1,145.54       $1,240.6736   $1,240.67   $1,240.65   $1,240.60