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	$216.36	3.526%	$223.9889	$223.99	$224.00	$224.00
Purchase #2	$94.49	7.792%	$101.8527	$101.85	$101.85	$101.90
Purchase #3	$214.25	4.348%	$223.5656	$223.57	$223.55	$223.60
Purchase #4	$18.36	11.780%	$20.5228	$20.52	$20.50	$20.50
Purchase #5	$70.72	6.443%	$75.2765	$75.28	$75.30	$75.30
Purchase #6	$85.37	6.409%	$90.8414	$90.84	$90.85	$90.80
Purchase #7	$210.88	7.282%	$226.2363	$226.24	$226.25	$226.20
7 purchase totals =	$910.43		$962.2842	$962.29	$962.30	$962.30