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	$40.35	6.826%	$43.1043	$43.10	$43.10	$43.10
Purchase #2	$159.88	7.121%	$171.2651	$171.27	$171.25	$171.30
Purchase #3	$70.77	3.606%	$73.322	$73.32	$73.30	$73.30
Purchase #4	$230.32	13.451%	$261.3003	$261.30	$261.30	$261.30
Purchase #5	$19.86	7.324%	$21.3145	$21.31	$21.30	$21.30
Purchase #6	$54.78	7.337%	$58.7992	$58.80	$58.80	$58.80
Purchase #7	$55.75	7.185%	$59.7556	$59.76	$59.75	$59.80
7 purchase totals =	$631.71		$688.8610	$688.86	$688.80	$688.90