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	$170.82	4.418%	$178.3668	$178.37	$178.35	$178.40
Purchase #2	$148.80	3.678%	$154.2729	$154.27	$154.25	$154.30
Purchase #3	$18.77	7.784%	$20.2311	$20.23	$20.25	$20.20
Purchase #4	$242.66	13.347%	$275.0478	$275.05	$275.05	$275.00
Purchase #5	$194.39	11.548%	$216.8382	$216.84	$216.85	$216.80
Purchase #6	$238.66	10.528%	$263.7861	$263.79	$263.80	$263.80
Purchase #7	$36.57	5.311%	$38.5122	$38.51	$38.50	$38.50
7 purchase totals =	$1,050.67		$1,147.0551	$1,147.06	$1,147.05	$1,147.00