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	$18.26	10.802%	$20.2324	$20.23	$20.25	$20.20
Purchase #2	$140.62	5.536%	$148.4047	$148.40	$148.40	$148.40
Purchase #3	$167.46	4.536%	$175.056	$175.06	$175.05	$175.10
Purchase #4	$78.59	4.435%	$82.0755	$82.08	$82.10	$82.10
Purchase #5	$223.37	3.404%	$230.9735	$230.97	$230.95	$231.00
Purchase #6	$210.39	10.137%	$231.7172	$231.72	$231.70	$231.70
Purchase #7	$178.91	6.634%	$190.7789	$190.78	$190.80	$190.80
7 purchase totals =	$1,017.60		$1,079.2382	$1,079.24	$1,079.25	$1,079.30