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	$27.68	7.598%	$29.7831	$29.78	$29.80	$29.80
Purchase #2	$250.42	11.826%	$280.0347	$280.03	$280.05	$280.00
Purchase #3	$92.79	8.549%	$100.7226	$100.72	$100.70	$100.70
Purchase #4	$225.70	9.760%	$247.7283	$247.73	$247.75	$247.70
Purchase #5	$70.52	10.595%	$77.9916	$77.99	$78.00	$78.00
Purchase #6	$170.32	11.238%	$189.4606	$189.46	$189.45	$189.50
Purchase #7	$73.76	12.748%	$83.1629	$83.16	$83.15	$83.20
7 purchase totals =	$911.19		$1,008.8838	$1,008.87	$1,008.90	$1,008.90