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	$243.78	4.787%	$255.4497	$255.45	$255.45	$255.40
Purchase #2	$45.70	11.359%	$50.8911	$50.89	$50.90	$50.90
Purchase #3	$190.74	10.505%	$210.7772	$210.78	$210.80	$210.80
Purchase #4	$238.57	12.720%	$268.9161	$268.92	$268.90	$268.90
Purchase #5	$166.84	10.307%	$184.0362	$184.04	$184.05	$184.00
Purchase #6	$92.61	13.439%	$105.0559	$105.06	$105.05	$105.10
Purchase #7	$153.96	10.337%	$169.8748	$169.87	$169.85	$169.90
7 purchase totals =	$1,132.20		$1,245.0010	$1,245.01	$1,245.00	$1,245.00