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	$79.57	12.645%	$89.6316	$89.63	$89.65	$89.60
Purchase #2	$44.31	10.337%	$48.8903	$48.89	$48.90	$48.90
Purchase #3	$12.74	6.846%	$13.6122	$13.61	$13.60	$13.60
Purchase #4	$134.91	13.434%	$153.0338	$153.03	$153.05	$153.00
Purchase #5	$97.78	11.751%	$109.2701	$109.27	$109.25	$109.30
Purchase #6	$185.56	13.209%	$210.0706	$210.07	$210.05	$210.10
Purchase #7	$164.86	9.118%	$179.8919	$179.89	$179.90	$179.90
7 purchase totals =	$719.73		$804.4005	$804.39	$804.40	$804.40