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	$154.96	12.852%	$174.8755	$174.88	$174.90	$174.90
Purchase #2	$124.63	12.550%	$140.2711	$140.27	$140.25	$140.30
Purchase #3	$35.59	13.106%	$40.2544	$40.25	$40.25	$40.30
Purchase #4	$206.44	7.539%	$222.0035	$222.00	$222.00	$222.00
Purchase #5	$225.27	3.546%	$233.2581	$233.26	$233.25	$233.30
Purchase #6	$44.47	13.784%	$50.5997	$50.60	$50.60	$50.60
Purchase #7	$52.62	10.162%	$57.9672	$57.97	$57.95	$58.00
7 purchase totals =	$843.98		$919.2295	$919.23	$919.20	$919.40