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	$160.91	7.847%	$173.5366	$173.54	$173.55	$173.50
Purchase #2	$133.67	6.700%	$142.6259	$142.63	$142.65	$142.60
Purchase #3	$231.51	5.375%	$243.9537	$243.95	$243.95	$244.00
Purchase #4	$65.74	10.495%	$72.6394	$72.64	$72.65	$72.60
Purchase #5	$80.28	11.490%	$89.5042	$89.50	$89.50	$89.50
Purchase #6	$135.37	12.252%	$151.9555	$151.96	$151.95	$152.00
Purchase #7	$153.47	7.373%	$164.7853	$164.79	$164.80	$164.80
7 purchase totals =	$960.95		$1,039.0006	$1,039.01	$1,039.05	$1,039.00