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	$54.46	12.860%	$61.4636	$61.46	$61.45	$61.50
Purchase #2	$49.29	9.164%	$53.8069	$53.81	$53.80	$53.80
Purchase #3	$108.51	9.401%	$118.711	$118.71	$118.70	$118.70
Purchase #4	$239.72	8.767%	$260.7363	$260.74	$260.75	$260.70
Purchase #5	$39.28	11.740%	$43.8915	$43.89	$43.90	$43.90
Purchase #6	$124.31	13.619%	$141.2398	$141.24	$141.25	$141.20
Purchase #7	$124.43	9.406%	$136.1339	$136.13	$136.15	$136.10
7 purchase totals =	$740.00		$815.9830	$815.98	$816.00	$815.90