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 $168.85   8.322%   $182.9017   $182.90   $182.90   $182.90  
  Purchase #2 $6.29   9.209%   $6.8692   $6.87   $6.85   $6.90  
  Purchase #3 $181.41   8.360%   $196.5759   $196.58   $196.60   $196.60  
  Purchase #4 $210.85   13.807%   $239.9621   $239.96   $239.95   $240.00  
  Purchase #5 $153.29   8.566%   $166.4208   $166.42   $166.40   $166.40  
  Purchase #6 $190.69   13.104%   $215.678   $215.68   $215.70   $215.70  
  Purchase #7 $5.83   12.306%   $6.5474   $6.55   $6.55   $6.50  
  7 purchase totals = $917.21       $1,014.9551   $1,014.96   $1,014.95   $1,015.00