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	$141.96	11.227%	$157.8978	$157.90	$157.90	$157.90
Purchase #2	$100.52	9.111%	$109.6784	$109.68	$109.70	$109.70
Purchase #3	$100.46	4.252%	$104.7316	$104.73	$104.75	$104.70
Purchase #4	$192.67	9.296%	$210.5806	$210.58	$210.60	$210.60
Purchase #5	$51.25	8.735%	$55.7267	$55.73	$55.75	$55.70
Purchase #6	$67.27	4.340%	$70.1895	$70.19	$70.20	$70.20
Purchase #7	$100.67	10.330%	$111.0692	$111.07	$111.05	$111.10
7 purchase totals =	$754.80		$819.8738	$819.88	$819.95	$819.90