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	$25.83	13.298%	$29.2649	$29.26	$29.25	$29.30
Purchase #2	$177.78	4.286%	$185.3997	$185.40	$185.40	$185.40
Purchase #3	$169.30	4.126%	$176.2853	$176.29	$176.30	$176.30
Purchase #4	$83.54	12.727%	$94.1721	$94.17	$94.15	$94.20
Purchase #5	$83.88	6.593%	$89.4102	$89.41	$89.40	$89.40
Purchase #6	$156.73	6.769%	$167.3391	$167.34	$167.35	$167.30
Purchase #7	$33.42	4.320%	$34.8637	$34.86	$34.85	$34.90
7 purchase totals =	$730.48		$776.7350	$776.73	$776.70	$776.80