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	$156.54	5.334%	$164.8898	$164.89	$164.90	$164.90
Purchase #2	$34.83	13.161%	$39.414	$39.41	$39.40	$39.40
Purchase #3	$209.30	6.404%	$222.7036	$222.70	$222.70	$222.70
Purchase #4	$24.97	12.468%	$28.0833	$28.08	$28.10	$28.10
Purchase #5	$159.69	9.255%	$174.4693	$174.47	$174.45	$174.50
Purchase #6	$51.91	6.429%	$55.2473	$55.25	$55.25	$55.20
Purchase #7	$158.77	9.106%	$173.2276	$173.23	$173.25	$173.20
7 purchase totals =	$796.01		$858.0349	$858.03	$858.05	$858.00