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	$79.52	6.314%	$84.5409	$84.54	$84.55	$84.50
Purchase #2	$191.27	12.689%	$215.5403	$215.54	$215.55	$215.50
Purchase #3	$40.92	5.143%	$43.0245	$43.02	$43.00	$43.00
Purchase #4	$151.72	6.420%	$161.4604	$161.46	$161.45	$161.50
Purchase #5	$51.52	8.244%	$55.7673	$55.77	$55.75	$55.80
Purchase #6	$176.85	6.437%	$188.2338	$188.23	$188.25	$188.20
Purchase #7	$29.75	10.144%	$32.7678	$32.77	$32.75	$32.80
7 purchase totals =	$721.55		$781.3350	$781.33	$781.30	$781.30