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	$97.78	11.745%	$109.2643	$109.26	$109.25	$109.30
Purchase #2	$58.91	5.161%	$61.9503	$61.95	$61.95	$62.00
Purchase #3	$103.48	3.171%	$106.7614	$106.76	$106.75	$106.80
Purchase #4	$52.85	11.548%	$58.9531	$58.95	$58.95	$59.00
Purchase #5	$74.77	3.641%	$77.4924	$77.49	$77.50	$77.50
Purchase #6	$60.75	9.115%	$66.2874	$66.29	$66.30	$66.30
Purchase #7	$177.91	4.255%	$185.4801	$185.48	$185.50	$185.50
7 purchase totals =	$626.45		$666.1890	$666.18	$666.20	$666.40