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	$27.42	8.274%	$29.6887	$29.69	$29.70	$29.70
Purchase #2	$42.28	4.341%	$44.1154	$44.12	$44.10	$44.10
Purchase #3	$247.46	10.637%	$273.7823	$273.78	$273.80	$273.80
Purchase #4	$173.88	6.585%	$185.33	$185.33	$185.35	$185.30
Purchase #5	$158.42	4.261%	$165.1703	$165.17	$165.15	$165.20
Purchase #6	$66.93	6.196%	$71.077	$71.08	$71.10	$71.10
Purchase #7	$128.55	4.498%	$134.3322	$134.33	$134.35	$134.30
7 purchase totals =	$844.94		$903.4959	$903.50	$903.55	$903.50