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	$28.67	3.530%	$29.6821	$29.68	$29.70	$29.70
Purchase #2	$249.25	12.386%	$280.1221	$280.12	$280.10	$280.10
Purchase #3	$149.72	8.324%	$162.1827	$162.18	$162.20	$162.20
Purchase #4	$85.74	4.338%	$89.4594	$89.46	$89.45	$89.50
Purchase #5	$18.90	8.820%	$20.567	$20.57	$20.55	$20.60
Purchase #6	$242.49	4.710%	$253.9113	$253.91	$253.90	$253.90
Purchase #7	$45.30	6.285%	$48.1471	$48.15	$48.15	$48.10
7 purchase totals =	$820.07		$884.0717	$884.07	$884.05	$884.10