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	$158.65	9.215%	$173.2696	$173.27	$173.25	$173.30
Purchase #2	$202.45	5.329%	$213.2386	$213.24	$213.25	$213.20
Purchase #3	$125.40	11.501%	$139.8223	$139.82	$139.80	$139.80
Purchase #4	$53.88	11.438%	$60.0428	$60.04	$60.05	$60.00
Purchase #5	$147.65	10.296%	$162.852	$162.85	$162.85	$162.90
Purchase #6	$45.48	6.693%	$48.524	$48.52	$48.50	$48.50
Purchase #7	$165.75	10.122%	$182.5272	$182.53	$182.55	$182.50
7 purchase totals =	$899.26		$980.2765	$980.27	$980.25	$980.20