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	$78.31	13.469%	$88.8576	$88.86	$88.85	$88.90
Purchase #2	$180.95	13.201%	$204.8372	$204.84	$204.85	$204.80
Purchase #3	$235.42	8.655%	$255.7956	$255.80	$255.80	$255.80
Purchase #4	$36.53	6.407%	$38.8705	$38.87	$38.85	$38.90
Purchase #5	$237.32	4.595%	$248.2249	$248.22	$248.20	$248.20
Purchase #6	$54.43	11.378%	$60.623	$60.62	$60.60	$60.60
Purchase #7	$107.92	10.683%	$119.4491	$119.45	$119.45	$119.40
7 purchase totals =	$930.88		$1,016.6579	$1,016.66	$1,016.60	$1,016.60