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	$199.44	11.768%	$222.9101	$222.91	$222.90	$222.90
Purchase #2	$211.85	13.191%	$239.7951	$239.80	$239.80	$239.80
Purchase #3	$139.97	8.107%	$151.3174	$151.32	$151.30	$151.30
Purchase #4	$137.68	5.335%	$145.0252	$145.03	$145.05	$145.00
Purchase #5	$85.28	4.688%	$89.2779	$89.28	$89.30	$89.30
Purchase #6	$84.69	4.199%	$88.2461	$88.25	$88.25	$88.20
Purchase #7	$176.91	5.547%	$186.7232	$186.72	$186.70	$186.70
7 purchase totals =	$1,035.82		$1,123.2950	$1,123.31	$1,123.30	$1,123.20