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	$98.37	4.774%	$103.0662	$103.07	$103.05	$103.10
Purchase #2	$13.51	6.179%	$14.3448	$14.34	$14.35	$14.30
Purchase #3	$12.76	8.602%	$13.8576	$13.86	$13.85	$13.90
Purchase #4	$25.51	9.277%	$27.8766	$27.88	$27.90	$27.90
Purchase #5	$172.44	6.158%	$183.0589	$183.06	$183.05	$183.10
Purchase #6	$22.53	3.521%	$23.3233	$23.32	$23.30	$23.30
Purchase #7	$146.89	10.486%	$162.2929	$162.29	$162.30	$162.30
7 purchase totals =	$492.01		$527.8203	$527.82	$527.80	$527.90