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 $214.71   12.544%   $241.6432   $241.64   $241.65   $241.60  
  Purchase #2 $213.77   5.405%   $225.3243   $225.32   $225.30   $225.30  
  Purchase #3 $206.80   11.516%   $230.6151   $230.62   $230.60   $230.60  
  Purchase #4 $207.40   8.780%   $225.6097   $225.61   $225.60   $225.60  
  Purchase #5 $133.92   10.678%   $148.22   $148.22   $148.20   $148.20  
  Purchase #6 $209.31   3.213%   $216.0351   $216.04   $216.05   $216.00  
  Purchase #7 $26.95   11.291%   $29.9929   $29.99   $30.00   $30.00  
  7 purchase totals = $1,212.86       $1,317.4403   $1,317.44   $1,317.40   $1,317.30