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	$181.44	4.861%	$190.2598	$190.26	$190.25	$190.30
Purchase #2	$82.67	10.822%	$91.6165	$91.62	$91.60	$91.60
Purchase #3	$172.36	7.646%	$185.5386	$185.54	$185.55	$185.50
Purchase #4	$83.74	5.801%	$88.5978	$88.60	$88.60	$88.60
Purchase #5	$153.58	12.581%	$172.9019	$172.90	$172.90	$172.90
Purchase #6	$106.67	9.243%	$116.5295	$116.53	$116.55	$116.50
Purchase #7	$247.37	13.673%	$281.1929	$281.19	$281.20	$281.20
7 purchase totals =	$1,027.83		$1,126.6370	$1,126.64	$1,126.65	$1,126.60