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	$104.87	6.109%	$111.2765	$111.28	$111.30	$111.30
Purchase #2	$238.52	5.216%	$250.9612	$250.96	$250.95	$251.00
Purchase #3	$165.79	4.128%	$172.6338	$172.63	$172.65	$172.60
Purchase #4	$7.81	6.151%	$8.2904	$8.29	$8.30	$8.30
Purchase #5	$177.68	3.330%	$183.5967	$183.60	$183.60	$183.60
Purchase #6	$11.59	10.796%	$12.8413	$12.84	$12.85	$12.80
Purchase #7	$48.79	6.373%	$51.8994	$51.90	$51.90	$51.90
7 purchase totals =	$755.05		$791.4993	$791.50	$791.55	$791.50