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	$232.40	11.866%	$259.9766	$259.98	$260.00	$260.00
Purchase #2	$90.75	6.511%	$96.6587	$96.66	$96.65	$96.70
Purchase #3	$201.92	13.791%	$229.7668	$229.77	$229.75	$229.80
Purchase #4	$99.60	5.585%	$105.1627	$105.16	$105.15	$105.20
Purchase #5	$165.79	6.533%	$176.6211	$176.62	$176.60	$176.60
Purchase #6	$167.66	13.468%	$190.2404	$190.24	$190.25	$190.20
Purchase #7	$97.68	3.289%	$100.8927	$100.89	$100.90	$100.90
7 purchase totals =	$1,055.80		$1,159.3190	$1,159.32	$1,159.30	$1,159.40