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	$42.57	6.300%	$45.2519	$45.25	$45.25	$45.30
Purchase #2	$47.71	12.560%	$53.7024	$53.70	$53.70	$53.70
Purchase #3	$95.27	8.827%	$103.6795	$103.68	$103.70	$103.70
Purchase #4	$105.61	3.557%	$109.3665	$109.37	$109.35	$109.40
Purchase #5	$141.67	11.842%	$158.4466	$158.45	$158.45	$158.40
Purchase #6	$62.66	13.649%	$71.2125	$71.21	$71.20	$71.20
Purchase #7	$49.50	7.853%	$53.3872	$53.39	$53.40	$53.40
7 purchase totals =	$544.99		$595.0466	$595.05	$595.05	$595.10