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	$19.94	4.721%	$20.8814	$20.88	$20.90	$20.90
Purchase #2	$156.69	7.613%	$168.6188	$168.62	$168.60	$168.60
Purchase #3	$32.28	11.776%	$36.0813	$36.08	$36.10	$36.10
Purchase #4	$26.63	6.372%	$28.3269	$28.33	$28.35	$28.30
Purchase #5	$80.40	3.621%	$83.3113	$83.31	$83.30	$83.30
Purchase #6	$17.96	4.510%	$18.77	$18.77	$18.75	$18.80
Purchase #7	$146.55	9.164%	$159.9798	$159.98	$160.00	$160.00
7 purchase totals =	$480.45		$515.9695	$515.97	$516.00	$516.00