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	$63.52	7.149%	$68.061	$68.06	$68.05	$68.10
Purchase #2	$83.30	7.860%	$89.8474	$89.85	$89.85	$89.80
Purchase #3	$85.78	11.600%	$95.7305	$95.73	$95.75	$95.70
Purchase #4	$212.30	4.704%	$222.2866	$222.29	$222.30	$222.30
Purchase #5	$239.71	8.604%	$260.3346	$260.33	$260.35	$260.30
Purchase #6	$58.36	12.251%	$65.5097	$65.51	$65.50	$65.50
Purchase #7	$159.55	13.542%	$181.1563	$181.16	$181.15	$181.20
7 purchase totals =	$902.52		$982.9261	$982.93	$982.95	$982.90