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	$5.94	8.542%	$6.4474	$6.45	$6.45	$6.40
Purchase #2	$178.83	4.333%	$186.5787	$186.58	$186.60	$186.60
Purchase #3	$106.87	4.223%	$111.3831	$111.38	$111.40	$111.40
Purchase #4	$56.99	3.718%	$59.1089	$59.11	$59.10	$59.10
Purchase #5	$64.52	10.325%	$71.1817	$71.18	$71.20	$71.20
Purchase #6	$82.93	8.291%	$89.8057	$89.81	$89.80	$89.80
Purchase #7	$30.27	3.770%	$31.4112	$31.41	$31.40	$31.40
7 purchase totals =	$526.35		$555.9167	$555.92	$555.95	$555.90