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	$79.94	12.625%	$90.0324	$90.03	$90.05	$90.00
Purchase #2	$241.42	9.728%	$264.9053	$264.91	$264.90	$264.90
Purchase #3	$173.53	6.558%	$184.9101	$184.91	$184.90	$184.90
Purchase #4	$182.58	13.870%	$207.9038	$207.90	$207.90	$207.90
Purchase #5	$55.59	3.118%	$57.3233	$57.32	$57.30	$57.30
Purchase #6	$10.92	3.436%	$11.2952	$11.30	$11.30	$11.30
Purchase #7	$186.42	8.637%	$202.5211	$202.52	$202.50	$202.50
7 purchase totals =	$930.40		$1,018.8912	$1,018.89	$1,018.85	$1,018.80