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	$75.45	5.365%	$79.4979	$79.50	$79.50	$79.50
Purchase #2	$180.82	5.325%	$190.4487	$190.45	$190.45	$190.40
Purchase #3	$204.57	10.784%	$226.6308	$226.63	$226.65	$226.60
Purchase #4	$154.35	6.422%	$164.2624	$164.26	$164.25	$164.30
Purchase #5	$111.81	3.495%	$115.7178	$115.72	$115.70	$115.70
Purchase #6	$171.69	11.216%	$190.9468	$190.95	$190.95	$190.90
Purchase #7	$52.79	12.791%	$59.5424	$59.54	$59.55	$59.50
7 purchase totals =	$951.48		$1,027.0468	$1,027.05	$1,027.05	$1,026.90