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	$80.55	11.648%	$89.9325	$89.93	$89.95	$89.90
Purchase #2	$153.50	8.682%	$166.8269	$166.83	$166.85	$166.80
Purchase #3	$76.93	13.751%	$87.5086	$87.51	$87.50	$87.50
Purchase #4	$119.69	6.341%	$127.2795	$127.28	$127.30	$127.30
Purchase #5	$23.46	3.833%	$24.3592	$24.36	$24.35	$24.40
Purchase #6	$49.38	9.679%	$54.1595	$54.16	$54.15	$54.20
Purchase #7	$140.95	6.621%	$150.2823	$150.28	$150.30	$150.30
7 purchase totals =	$644.46		$700.3485	$700.35	$700.40	$700.40