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	$188.49	11.845%	$210.8166	$210.82	$210.80	$210.80
Purchase #2	$18.66	9.420%	$20.4178	$20.42	$20.40	$20.40
Purchase #3	$53.57	13.194%	$60.638	$60.64	$60.65	$60.60
Purchase #4	$58.60	10.446%	$64.7214	$64.72	$64.70	$64.70
Purchase #5	$87.89	10.563%	$97.1738	$97.17	$97.15	$97.20
Purchase #6	$86.31	5.152%	$90.7567	$90.76	$90.75	$90.80
Purchase #7	$222.81	10.158%	$245.443	$245.44	$245.45	$245.40
7 purchase totals =	$716.33		$789.9673	$789.97	$789.90	$789.90