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 $214.34   12.527%   $241.1904   $241.19   $241.20   $241.20  
  Purchase #2 $197.30   4.403%   $205.9871   $205.99   $206.00   $206.00  
  Purchase #3 $230.76   4.857%   $241.968   $241.97   $241.95   $242.00  
  Purchase #4 $92.81   8.141%   $100.3657   $100.37   $100.35   $100.40  
  Purchase #5 $250.93   12.775%   $282.9863   $282.99   $283.00   $283.00  
  Purchase #6 $17.79   6.494%   $18.9453   $18.95   $18.95   $18.90  
  Purchase #7 $230.70   9.196%   $251.9152   $251.92   $251.90   $251.90  
  7 purchase totals = $1,234.63       $1,343.3580   $1,343.38   $1,343.35   $1,343.40