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	$130.42	11.717%	$145.7013	$145.70	$145.70	$145.70
Purchase #2	$28.50	3.333%	$29.4499	$29.45	$29.45	$29.40
Purchase #3	$106.94	13.115%	$120.9652	$120.97	$120.95	$121.00
Purchase #4	$57.60	8.585%	$62.545	$62.55	$62.55	$62.50
Purchase #5	$27.89	3.199%	$28.7822	$28.78	$28.80	$28.80
Purchase #6	$180.85	5.286%	$190.4097	$190.41	$190.40	$190.40
Purchase #7	$208.31	6.848%	$222.5751	$222.58	$222.60	$222.60
7 purchase totals =	$740.51		$800.4284	$800.44	$800.45	$800.40