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	$131.88	4.662%	$138.0282	$138.03	$138.05	$138.00
Purchase #2	$36.94	4.335%	$38.5413	$38.54	$38.55	$38.50
Purchase #3	$158.43	11.794%	$177.1152	$177.12	$177.10	$177.10
Purchase #4	$12.75	6.503%	$13.5791	$13.58	$13.60	$13.60
Purchase #5	$78.69	4.385%	$82.1406	$82.14	$82.15	$82.10
Purchase #6	$154.98	12.478%	$174.3184	$174.32	$174.30	$174.30
Purchase #7	$79.72	12.479%	$89.6683	$89.67	$89.65	$89.70
7 purchase totals =	$653.39		$713.3911	$713.40	$713.40	$713.30