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	$26.51	9.859%	$29.1236	$29.12	$29.10	$29.10
Purchase #2	$157.61	4.209%	$164.2438	$164.24	$164.25	$164.20
Purchase #3	$103.49	7.573%	$111.3273	$111.33	$111.35	$111.30
Purchase #4	$18.78	5.761%	$19.8619	$19.86	$19.85	$19.90
Purchase #5	$198.91	7.192%	$213.2156	$213.22	$213.20	$213.20
Purchase #6	$158.43	9.656%	$173.728	$173.73	$173.75	$173.70
Purchase #7	$38.27	12.507%	$43.0564	$43.06	$43.05	$43.10
7 purchase totals =	$702.00		$754.5566	$754.56	$754.55	$754.50