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	$250.83	4.809%	$262.8924	$262.89	$262.90	$262.90
Purchase #2	$225.91	13.244%	$255.8295	$255.83	$255.85	$255.80
Purchase #3	$91.89	11.347%	$102.3168	$102.32	$102.30	$102.30
Purchase #4	$215.52	11.477%	$240.2552	$240.26	$240.25	$240.30
Purchase #5	$197.25	5.387%	$207.8759	$207.88	$207.90	$207.90
Purchase #6	$242.75	13.634%	$275.8465	$275.85	$275.85	$275.80
Purchase #7	$123.33	11.560%	$137.5869	$137.59	$137.60	$137.60
7 purchase totals =	$1,347.48		$1,482.6032	$1,482.62	$1,482.65	$1,482.60