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	$39.81	6.551%	$42.418	$42.42	$42.40	$42.40
Purchase #2	$13.71	12.667%	$15.4466	$15.45	$15.45	$15.40
Purchase #3	$5.81	6.234%	$6.1722	$6.17	$6.15	$6.20
Purchase #4	$52.72	10.656%	$58.3378	$58.34	$58.35	$58.30
Purchase #5	$72.37	11.110%	$80.4103	$80.41	$80.40	$80.40
Purchase #6	$101.87	9.173%	$111.2145	$111.21	$111.20	$111.20
Purchase #7	$151.31	6.512%	$161.1633	$161.16	$161.15	$161.20
7 purchase totals =	$437.60		$475.1627	$475.16	$475.10	$475.10