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	$75.77	3.166%	$78.1689	$78.17	$78.15	$78.20
Purchase #2	$9.72	5.228%	$10.2282	$10.23	$10.25	$10.20
Purchase #3	$192.32	4.127%	$200.257	$200.26	$200.25	$200.30
Purchase #4	$37.26	6.495%	$39.68	$39.68	$39.70	$39.70
Purchase #5	$158.47	7.110%	$169.7372	$169.74	$169.75	$169.70
Purchase #6	$173.63	3.346%	$179.4397	$179.44	$179.45	$179.40
Purchase #7	$100.81	10.740%	$111.637	$111.64	$111.65	$111.60
7 purchase totals =	$747.98		$789.1480	$789.16	$789.20	$789.10