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	$22.77	9.811%	$25.004	$25.00	$25.00	$25.00
Purchase #2	$40.30	11.204%	$44.8152	$44.82	$44.80	$44.80
Purchase #3	$86.48	3.146%	$89.2007	$89.20	$89.20	$89.20
Purchase #4	$173.93	6.852%	$185.8477	$185.85	$185.85	$185.80
Purchase #5	$46.51	11.219%	$51.728	$51.73	$51.75	$51.70
Purchase #6	$153.65	8.636%	$166.9192	$166.92	$166.90	$166.90
Purchase #7	$152.98	12.452%	$172.0291	$172.03	$172.05	$172.00
7 purchase totals =	$676.62		$735.5439	$735.55	$735.55	$735.40