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 $20.88   7.663%   $22.48   $22.48   $22.50   $22.50  
  Purchase #2 $105.46   9.559%   $115.5409   $115.54   $115.55   $115.50  
  Purchase #3 $131.29   8.700%   $142.7122   $142.71   $142.70   $142.70  
  Purchase #4 $19.67   11.838%   $21.9985   $22.00   $22.00   $22.00  
  Purchase #5 $52.28   10.565%   $57.8034   $57.80   $57.80   $57.80  
  Purchase #6 $235.64   7.361%   $252.9855   $252.99   $253.00   $253.00  
  Purchase #7 $17.30   5.858%   $18.3134   $18.31   $18.30   $18.30  
  7 purchase totals = $582.52       $631.8339   $631.83   $631.85   $631.80