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	$111.72	5.243%	$117.5775	$117.58	$117.60	$117.60
Purchase #2	$48.87	8.752%	$53.1471	$53.15	$53.15	$53.10
Purchase #3	$115.90	12.525%	$130.4165	$130.42	$130.40	$130.40
Purchase #4	$108.39	4.859%	$113.6567	$113.66	$113.65	$113.70
Purchase #5	$48.76	10.528%	$53.8935	$53.89	$53.90	$53.90
Purchase #6	$25.34	8.172%	$27.4108	$27.41	$27.40	$27.40
Purchase #7	$153.67	11.193%	$170.8703	$170.87	$170.85	$170.90
7 purchase totals =	$612.65		$666.9724	$666.98	$666.95	$667.00