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	$56.54	8.613%	$61.4098	$61.41	$61.40	$61.40
Purchase #2	$81.60	4.820%	$85.5331	$85.53	$85.55	$85.50
Purchase #3	$177.47	3.522%	$183.7205	$183.72	$183.70	$183.70
Purchase #4	$210.71	3.150%	$217.3474	$217.35	$217.35	$217.30
Purchase #5	$153.34	11.632%	$171.1765	$171.18	$171.20	$171.20
Purchase #6	$82.74	8.734%	$89.9665	$89.97	$89.95	$90.00
Purchase #7	$15.40	3.282%	$15.9054	$15.91	$15.90	$15.90
7 purchase totals =	$777.80		$825.0592	$825.07	$825.05	$825.00