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 $246.49   8.338%   $267.0423   $267.04   $267.05   $267.00  
  Purchase #2 $244.57   7.681%   $263.3554   $263.36   $263.35   $263.40  
  Purchase #3 $86.32   6.109%   $91.5933   $91.59   $91.60   $91.60  
  Purchase #4 $98.54   3.136%   $101.6302   $101.63   $101.65   $101.60  
  Purchase #5 $191.26   7.106%   $204.8509   $204.85   $204.85   $204.90  
  Purchase #6 $122.94   11.375%   $136.9244   $136.92   $136.90   $136.90  
  Purchase #7 $69.84   11.512%   $77.88   $77.88   $77.90   $77.90  
  7 purchase totals = $1,059.96       $1,143.2765   $1,143.27   $1,143.30   $1,143.30