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	$238.92	5.420%	$251.8695	$251.87	$251.85	$251.90
Purchase #2	$166.58	12.235%	$186.9611	$186.96	$186.95	$187.00
Purchase #3	$39.69	3.832%	$41.2109	$41.21	$41.20	$41.20
Purchase #4	$105.40	4.247%	$109.8763	$109.88	$109.90	$109.90
Purchase #5	$77.89	6.253%	$82.7605	$82.76	$82.75	$82.80
Purchase #6	$120.37	11.643%	$134.3847	$134.38	$134.40	$134.40
Purchase #7	$80.69	6.197%	$85.6904	$85.69	$85.70	$85.70
7 purchase totals =	$829.54		$892.7534	$892.75	$892.75	$892.90