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	$153.41	9.788%	$168.4258	$168.43	$168.45	$168.40
Purchase #2	$129.25	6.679%	$137.8826	$137.88	$137.90	$137.90
Purchase #3	$234.91	7.432%	$252.3685	$252.37	$252.35	$252.40
Purchase #4	$35.59	5.568%	$37.5717	$37.57	$37.55	$37.60
Purchase #5	$216.41	10.123%	$238.3172	$238.32	$238.30	$238.30
Purchase #6	$230.45	10.470%	$254.5781	$254.58	$254.60	$254.60
Purchase #7	$159.48	10.649%	$176.463	$176.46	$176.45	$176.50
7 purchase totals =	$1,159.50		$1,265.6069	$1,265.61	$1,265.60	$1,265.70