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	$144.85	7.336%	$155.4762	$155.48	$155.50	$155.50
Purchase #2	$57.75	3.243%	$59.6228	$59.62	$59.60	$59.60
Purchase #3	$85.55	5.179%	$89.9806	$89.98	$90.00	$90.00
Purchase #4	$103.39	8.648%	$112.3312	$112.33	$112.35	$112.30
Purchase #5	$62.95	10.268%	$69.4137	$69.41	$69.40	$69.40
Purchase #6	$104.45	10.329%	$115.2386	$115.24	$115.25	$115.20
Purchase #7	$223.76	6.383%	$238.0426	$238.04	$238.05	$238.00
7 purchase totals =	$782.70		$840.1057	$840.10	$840.15	$840.00