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	$100.89	10.122%	$111.1021	$111.10	$111.10	$111.10
Purchase #2	$245.30	9.535%	$268.6894	$268.69	$268.70	$268.70
Purchase #3	$249.90	7.256%	$268.0327	$268.03	$268.05	$268.00
Purchase #4	$231.92	10.321%	$255.8565	$255.86	$255.85	$255.90
Purchase #5	$158.33	11.848%	$177.0889	$177.09	$177.10	$177.10
Purchase #6	$202.81	3.767%	$210.4499	$210.45	$210.45	$210.40
Purchase #7	$238.80	10.833%	$264.6692	$264.67	$264.65	$264.70
7 purchase totals =	$1,427.95		$1,555.8887	$1,555.89	$1,555.90	$1,555.90