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	$82.52	8.642%	$89.6514	$89.65	$89.65	$89.70
Purchase #2	$149.25	6.677%	$159.2154	$159.22	$159.20	$159.20
Purchase #3	$221.37	12.327%	$248.6583	$248.66	$248.65	$248.70
Purchase #4	$152.98	3.692%	$158.628	$158.63	$158.65	$158.60
Purchase #5	$171.69	13.737%	$195.2751	$195.28	$195.30	$195.30
Purchase #6	$51.30	5.826%	$54.2887	$54.29	$54.30	$54.30
Purchase #7	$163.78	4.438%	$171.0486	$171.05	$171.05	$171.00
7 purchase totals =	$992.89		$1,076.7655	$1,076.78	$1,076.80	$1,076.80