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	$131.41	8.453%	$142.5181	$142.52	$142.50	$142.50
Purchase #2	$141.35	10.234%	$155.8158	$155.82	$155.80	$155.80
Purchase #3	$52.98	4.224%	$55.2179	$55.22	$55.20	$55.20
Purchase #4	$171.60	13.255%	$194.3456	$194.35	$194.35	$194.30
Purchase #5	$156.40	13.627%	$177.7126	$177.71	$177.70	$177.70
Purchase #6	$86.33	3.259%	$89.1435	$89.14	$89.15	$89.10
Purchase #7	$17.32	4.157%	$18.04	$18.04	$18.05	$18.00
7 purchase totals =	$757.39		$832.7935	$832.80	$832.75	$832.60