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	$145.62	9.374%	$159.2704	$159.27	$159.25	$159.30
Purchase #2	$131.97	12.791%	$148.8503	$148.85	$148.85	$148.90
Purchase #3	$94.32	10.563%	$104.283	$104.28	$104.30	$104.30
Purchase #4	$97.91	5.718%	$103.5085	$103.51	$103.50	$103.50
Purchase #5	$71.34	8.572%	$77.4553	$77.46	$77.45	$77.50
Purchase #6	$43.39	7.492%	$46.6408	$46.64	$46.65	$46.60
Purchase #7	$179.76	8.784%	$195.5501	$195.55	$195.55	$195.60
7 purchase totals =	$764.31		$835.5584	$835.56	$835.55	$835.70