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	$68.65	13.856%	$78.1621	$78.16	$78.15	$78.20
Purchase #2	$239.34	7.195%	$256.5605	$256.56	$256.55	$256.60
Purchase #3	$170.28	7.778%	$183.5244	$183.52	$183.50	$183.50
Purchase #4	$172.81	9.133%	$188.5927	$188.59	$188.60	$188.60
Purchase #5	$135.68	9.285%	$148.2779	$148.28	$148.30	$148.30
Purchase #6	$137.40	4.334%	$143.3549	$143.35	$143.35	$143.40
Purchase #7	$250.39	11.851%	$280.0637	$280.06	$280.05	$280.10
7 purchase totals =	$1,174.55		$1,278.5362	$1,278.52	$1,278.50	$1,278.70