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	$94.56	5.543%	$99.8015	$99.80	$99.80	$99.80
Purchase #2	$149.96	10.741%	$166.0672	$166.07	$166.05	$166.10
Purchase #3	$237.31	13.149%	$268.5139	$268.51	$268.50	$268.50
Purchase #4	$167.51	3.749%	$173.7899	$173.79	$173.80	$173.80
Purchase #5	$88.28	8.345%	$95.647	$95.65	$95.65	$95.60
Purchase #6	$229.38	5.192%	$241.2894	$241.29	$241.30	$241.30
Purchase #7	$37.73	10.653%	$41.7494	$41.75	$41.75	$41.70
7 purchase totals =	$1,004.73		$1,086.8583	$1,086.86	$1,086.85	$1,086.80