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	$219.83	9.432%	$240.5644	$240.56	$240.55	$240.60
Purchase #2	$35.41	6.643%	$37.7623	$37.76	$37.75	$37.80
Purchase #3	$104.46	7.466%	$112.259	$112.26	$112.25	$112.30
Purchase #4	$127.29	3.610%	$131.8852	$131.89	$131.90	$131.90
Purchase #5	$70.65	9.836%	$77.5991	$77.60	$77.60	$77.60
Purchase #6	$63.84	10.648%	$70.6377	$70.64	$70.65	$70.60
Purchase #7	$235.74	5.583%	$248.9014	$248.90	$248.90	$248.90
7 purchase totals =	$857.22		$919.6091	$919.61	$919.60	$919.70