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	$223.65	3.557%	$231.6052	$231.61	$231.60	$231.60
Purchase #2	$120.83	9.593%	$132.4212	$132.42	$132.40	$132.40
Purchase #3	$99.36	12.481%	$111.7611	$111.76	$111.75	$111.80
Purchase #4	$67.35	5.535%	$71.0778	$71.08	$71.10	$71.10
Purchase #5	$95.32	13.552%	$108.2378	$108.24	$108.25	$108.20
Purchase #6	$65.84	7.155%	$70.5509	$70.55	$70.55	$70.60
Purchase #7	$243.60	11.493%	$271.5969	$271.60	$271.60	$271.60
7 purchase totals =	$915.95		$997.2509	$997.26	$997.25	$997.30