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 $168.83   10.802%   $187.067   $187.07   $187.05   $187.10  
  Purchase #2 $181.85   9.609%   $199.324   $199.32   $199.30   $199.30  
  Purchase #3 $130.62   4.537%   $136.5462   $136.55   $136.55   $136.50  
  Purchase #4 $199.36   12.342%   $223.965   $223.97   $223.95   $224.00  
  Purchase #5 $181.81   7.556%   $195.5476   $195.55   $195.55   $195.50  
  Purchase #6 $193.26   12.605%   $217.6204   $217.62   $217.60   $217.60  
  Purchase #7 $210.25   9.824%   $230.905   $230.91   $230.90   $230.90  
  7 purchase totals = $1,265.98       $1,390.9752   $1,390.99   $1,390.90   $1,390.90