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	$239.46	10.287%	$264.0933	$264.09	$264.10	$264.10
Purchase #2	$211.72	13.128%	$239.5146	$239.51	$239.50	$239.50
Purchase #3	$188.73	11.489%	$210.4132	$210.41	$210.40	$210.40
Purchase #4	$52.45	11.781%	$58.6291	$58.63	$58.65	$58.60
Purchase #5	$61.39	6.469%	$65.3613	$65.36	$65.35	$65.40
Purchase #6	$99.25	12.664%	$111.819	$111.82	$111.80	$111.80
Purchase #7	$247.25	13.271%	$280.0625	$280.06	$280.05	$280.10
7 purchase totals =	$1,100.25		$1,229.8930	$1,229.88	$1,229.85	$1,229.90