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	$85.38	6.470%	$90.9041	$90.90	$90.90	$90.90
Purchase #2	$144.29	8.523%	$156.5878	$156.59	$156.60	$156.60
Purchase #3	$188.43	8.499%	$204.4447	$204.44	$204.45	$204.40
Purchase #4	$200.80	9.203%	$219.2796	$219.28	$219.30	$219.30
Purchase #5	$107.89	4.404%	$112.6415	$112.64	$112.65	$112.60
Purchase #6	$56.28	4.614%	$58.8768	$58.88	$58.90	$58.90
Purchase #7	$108.60	4.177%	$113.1362	$113.14	$113.15	$113.10
7 purchase totals =	$891.67		$955.8707	$955.87	$955.95	$955.80