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 $244.70   11.372%   $272.5273   $272.53   $272.55   $272.50  
  Purchase #2 $204.98   9.355%   $224.1559   $224.16   $224.15   $224.20  
  Purchase #3 $218.28   9.233%   $238.4338   $238.43   $238.45   $238.40  
  Purchase #4 $132.46   5.539%   $139.797   $139.80   $139.80   $139.80  
  Purchase #5 $229.83   4.704%   $240.6412   $240.64   $240.65   $240.60  
  Purchase #6 $19.70   13.153%   $22.2911   $22.29   $22.30   $22.30  
  Purchase #7 $221.39   3.828%   $229.8648   $229.86   $229.85   $229.90  
  7 purchase totals = $1,271.34       $1,367.7111   $1,367.71   $1,367.75   $1,367.70