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	$66.82	4.865%	$70.0708	$70.07	$70.05	$70.10
Purchase #2	$69.78	4.276%	$72.7638	$72.76	$72.75	$72.80
Purchase #3	$167.60	5.644%	$177.0593	$177.06	$177.05	$177.10
Purchase #4	$6.50	11.312%	$7.2353	$7.24	$7.25	$7.20
Purchase #5	$204.48	12.152%	$229.3284	$229.33	$229.35	$229.30
Purchase #6	$87.55	13.428%	$99.3062	$99.31	$99.30	$99.30
Purchase #7	$169.50	8.509%	$183.9228	$183.92	$183.90	$183.90
7 purchase totals =	$772.23		$839.6866	$839.69	$839.65	$839.70