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 $216.60   11.270%   $241.0108   $241.01   $241.00   $241.00  
  Purchase #2 $148.46   6.529%   $158.153   $158.15   $158.15   $158.20  
  Purchase #3 $15.84   7.668%   $17.0546   $17.05   $17.05   $17.10  
  Purchase #4 $242.88   6.680%   $259.1044   $259.10   $259.10   $259.10  
  Purchase #5 $250.44   5.776%   $264.9054   $264.91   $264.90   $264.90  
  Purchase #6 $125.39   13.509%   $142.3289   $142.33   $142.35   $142.30  
  Purchase #7 $195.32   10.484%   $215.7973   $215.80   $215.80   $215.80  
  7 purchase totals = $1,194.93       $1,298.3544   $1,298.35   $1,298.35   $1,298.40