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	$20.61	6.806%	$22.0127	$22.01	$22.00	$22.00
Purchase #2	$175.46	7.441%	$188.516	$188.52	$188.50	$188.50
Purchase #3	$71.63	10.481%	$79.1375	$79.14	$79.15	$79.10
Purchase #4	$94.32	4.452%	$98.5191	$98.52	$98.50	$98.50
Purchase #5	$229.89	11.151%	$255.525	$255.53	$255.55	$255.50
Purchase #6	$11.45	11.540%	$12.7713	$12.77	$12.75	$12.80
Purchase #7	$155.80	4.304%	$162.5056	$162.51	$162.50	$162.50
7 purchase totals =	$759.16		$818.9872	$819.00	$818.95	$818.90