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	$25.70	10.200%	$28.3214	$28.32	$28.30	$28.30
Purchase #2	$54.99	8.640%	$59.7411	$59.74	$59.75	$59.70
Purchase #3	$123.33	3.410%	$127.5356	$127.54	$127.55	$127.50
Purchase #4	$158.46	5.842%	$167.7172	$167.72	$167.70	$167.70
Purchase #5	$99.48	9.130%	$108.5625	$108.56	$108.55	$108.60
Purchase #6	$238.37	10.354%	$263.0508	$263.05	$263.05	$263.10
Purchase #7	$105.35	6.828%	$112.5433	$112.54	$112.55	$112.50
7 purchase totals =	$805.68		$867.4719	$867.47	$867.45	$867.40