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	$72.87	11.838%	$81.4964	$81.50	$81.50	$81.50
Purchase #2	$90.95	9.801%	$99.864	$99.86	$99.85	$99.90
Purchase #3	$221.77	3.677%	$229.9245	$229.92	$229.90	$229.90
Purchase #4	$109.94	4.664%	$115.0676	$115.07	$115.05	$115.10
Purchase #5	$20.97	7.259%	$22.4922	$22.49	$22.50	$22.50
Purchase #6	$132.26	7.763%	$142.5273	$142.53	$142.55	$142.50
Purchase #7	$245.82	5.123%	$258.4134	$258.41	$258.40	$258.40
7 purchase totals =	$894.58		$949.7854	$949.78	$949.75	$949.80