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	$5.82	4.661%	$6.0913	$6.09	$6.10	$6.10
Purchase #2	$112.62	5.847%	$119.2049	$119.20	$119.20	$119.20
Purchase #3	$9.79	3.155%	$10.0989	$10.10	$10.10	$10.10
Purchase #4	$96.25	7.383%	$103.3561	$103.36	$103.35	$103.40
Purchase #5	$223.70	6.613%	$238.4933	$238.49	$238.50	$238.50
Purchase #6	$145.44	13.869%	$165.6111	$165.61	$165.60	$165.60
Purchase #7	$159.56	12.568%	$179.6135	$179.61	$179.60	$179.60
7 purchase totals =	$753.18		$822.4691	$822.46	$822.45	$822.50