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	$52.83	6.206%	$56.1086	$56.11	$56.10	$56.10
Purchase #2	$243.82	9.452%	$266.8659	$266.87	$266.85	$266.90
Purchase #3	$160.64	7.309%	$172.3812	$172.38	$172.40	$172.40
Purchase #4	$103.79	3.200%	$107.1113	$107.11	$107.10	$107.10
Purchase #5	$19.52	7.357%	$20.9561	$20.96	$20.95	$21.00
Purchase #6	$85.56	4.469%	$89.3837	$89.38	$89.40	$89.40
Purchase #7	$250.28	4.197%	$260.7843	$260.78	$260.80	$260.80
7 purchase totals =	$916.44		$973.5911	$973.59	$973.60	$973.70