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	$18.54	9.639%	$20.3271	$20.33	$20.35	$20.30
Purchase #2	$58.73	5.440%	$61.9249	$61.92	$61.90	$61.90
Purchase #3	$174.44	8.509%	$189.2831	$189.28	$189.30	$189.30
Purchase #4	$246.99	7.384%	$265.2277	$265.23	$265.25	$265.20
Purchase #5	$48.44	4.152%	$50.4512	$50.45	$50.45	$50.50
Purchase #6	$47.97	12.768%	$54.0948	$54.09	$54.10	$54.10
Purchase #7	$247.75	4.776%	$259.5825	$259.58	$259.60	$259.60
7 purchase totals =	$842.86		$900.8913	$900.88	$900.95	$900.90