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	$217.37	7.324%	$233.2902	$233.29	$233.30	$233.30
Purchase #2	$55.88	9.499%	$61.188	$61.19	$61.20	$61.20
Purchase #3	$162.50	5.132%	$170.8395	$170.84	$170.85	$170.80
Purchase #4	$18.80	9.534%	$20.5924	$20.59	$20.60	$20.60
Purchase #5	$61.83	4.113%	$64.3731	$64.37	$64.35	$64.40
Purchase #6	$207.39	7.820%	$223.6079	$223.61	$223.60	$223.60
Purchase #7	$132.25	4.712%	$138.4816	$138.48	$138.50	$138.50
7 purchase totals =	$856.02		$912.3727	$912.37	$912.40	$912.40