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	$223.88	12.380%	$251.5963	$251.60	$251.60	$251.60
Purchase #2	$60.52	3.484%	$62.6285	$62.63	$62.65	$62.60
Purchase #3	$219.90	3.275%	$227.1017	$227.10	$227.10	$227.10
Purchase #4	$51.51	5.786%	$54.4904	$54.49	$54.50	$54.50
Purchase #5	$247.41	13.129%	$279.8925	$279.89	$279.90	$279.90
Purchase #6	$152.92	7.741%	$164.7575	$164.76	$164.75	$164.80
Purchase #7	$177.96	12.732%	$200.6179	$200.62	$200.60	$200.60
7 purchase totals =	$1,134.10		$1,241.0848	$1,241.09	$1,241.10	$1,241.10