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	$81.64	12.873%	$92.1495	$92.15	$92.15	$92.10
Purchase #2	$179.39	3.259%	$185.2363	$185.24	$185.25	$185.20
Purchase #3	$133.85	13.557%	$151.996	$152.00	$152.00	$152.00
Purchase #4	$20.65	9.788%	$22.6712	$22.67	$22.65	$22.70
Purchase #5	$98.70	13.140%	$111.6692	$111.67	$111.65	$111.70
Purchase #6	$123.61	9.109%	$134.8696	$134.87	$134.85	$134.90
Purchase #7	$212.38	13.277%	$240.5777	$240.58	$240.60	$240.60
7 purchase totals =	$850.22		$939.1695	$939.18	$939.15	$939.20