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	$150.66	12.563%	$169.5874	$169.59	$169.60	$169.60
Purchase #2	$35.42	6.114%	$37.5856	$37.59	$37.60	$37.60
Purchase #3	$152.38	13.637%	$173.1601	$173.16	$173.15	$173.20
Purchase #4	$131.61	5.148%	$138.3853	$138.39	$138.40	$138.40
Purchase #5	$107.87	11.374%	$120.1391	$120.14	$120.15	$120.10
Purchase #6	$129.33	5.748%	$136.7639	$136.76	$136.75	$136.80
Purchase #7	$106.84	4.296%	$111.4298	$111.43	$111.45	$111.40
7 purchase totals =	$814.11		$887.0512	$887.06	$887.10	$887.10