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	$80.44	12.121%	$90.1901	$90.19	$90.20	$90.20
Purchase #2	$55.25	11.567%	$61.6408	$61.64	$61.65	$61.60
Purchase #3	$87.98	6.317%	$93.5377	$93.54	$93.55	$93.50
Purchase #4	$241.37	7.114%	$258.5411	$258.54	$258.55	$258.50
Purchase #5	$218.25	3.349%	$225.5592	$225.56	$225.55	$225.60
Purchase #6	$125.52	13.670%	$142.6786	$142.68	$142.70	$142.70
Purchase #7	$35.41	8.569%	$38.4443	$38.44	$38.45	$38.40
7 purchase totals =	$844.22		$910.5918	$910.59	$910.65	$910.50