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	$24.58	12.137%	$27.5633	$27.56	$27.55	$27.60
Purchase #2	$53.45	10.406%	$59.012	$59.01	$59.00	$59.00
Purchase #3	$53.49	12.656%	$60.2597	$60.26	$60.25	$60.30
Purchase #4	$158.76	5.442%	$167.3997	$167.40	$167.40	$167.40
Purchase #5	$210.77	10.757%	$233.4425	$233.44	$233.45	$233.40
Purchase #6	$67.65	13.294%	$76.6434	$76.64	$76.65	$76.60
Purchase #7	$232.86	4.747%	$243.9139	$243.91	$243.90	$243.90
7 purchase totals =	$801.56		$868.2345	$868.22	$868.20	$868.20