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	$99.37	13.766%	$113.0493	$113.05	$113.05	$113.00
Purchase #2	$239.65	12.518%	$269.6494	$269.65	$269.65	$269.60
Purchase #3	$86.72	3.212%	$89.5054	$89.51	$89.50	$89.50
Purchase #4	$32.54	11.537%	$36.2941	$36.29	$36.30	$36.30
Purchase #5	$6.80	13.138%	$7.6934	$7.69	$7.70	$7.70
Purchase #6	$138.60	11.309%	$154.2743	$154.27	$154.25	$154.30
Purchase #7	$120.71	5.861%	$127.7848	$127.78	$127.80	$127.80
7 purchase totals =	$724.39		$798.2507	$798.24	$798.25	$798.20