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 $242.98   10.545%   $268.6022   $268.60   $268.60   $268.60  
  Purchase #2 $93.46   8.186%   $101.1106   $101.11   $101.10   $101.10  
  Purchase #3 $98.64   9.648%   $108.1568   $108.16   $108.15   $108.20  
  Purchase #4 $166.49   8.850%   $181.2244   $181.22   $181.20   $181.20  
  Purchase #5 $224.75   7.466%   $241.5298   $241.53   $241.55   $241.50  
  Purchase #6 $231.41   6.739%   $247.0047   $247.00   $247.00   $247.00  
  Purchase #7 $198.84   9.596%   $217.9207   $217.92   $217.90   $217.90  
  7 purchase totals = $1,256.57       $1,365.5492   $1,365.54   $1,365.50   $1,365.50