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	$175.39	6.178%	$186.2256	$186.23	$186.25	$186.20
Purchase #2	$211.74	8.170%	$229.0392	$229.04	$229.05	$229.00
Purchase #3	$161.77	6.478%	$172.2495	$172.25	$172.25	$172.20
Purchase #4	$48.80	10.723%	$54.0328	$54.03	$54.05	$54.00
Purchase #5	$66.71	12.139%	$74.8079	$74.81	$74.80	$74.80
Purchase #6	$92.67	12.523%	$104.2751	$104.28	$104.30	$104.30
Purchase #7	$171.27	8.164%	$185.2525	$185.25	$185.25	$185.30
7 purchase totals =	$928.35		$1,005.8826	$1,005.89	$1,005.95	$1,005.80