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	$80.45	10.662%	$89.0276	$89.03	$89.05	$89.00
Purchase #2	$30.60	4.227%	$31.8935	$31.89	$31.90	$31.90
Purchase #3	$145.69	7.470%	$156.573	$156.57	$156.55	$156.60
Purchase #4	$11.78	8.666%	$12.8009	$12.80	$12.80	$12.80
Purchase #5	$65.54	6.737%	$69.9554	$69.96	$69.95	$70.00
Purchase #6	$145.70	9.161%	$159.0476	$159.05	$159.05	$159.00
Purchase #7	$158.86	5.281%	$167.2494	$167.25	$167.25	$167.20
7 purchase totals =	$638.62		$686.5474	$686.55	$686.55	$686.50