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	$69.30	12.703%	$78.1032	$78.10	$78.10	$78.10
Purchase #2	$34.55	10.474%	$38.1688	$38.17	$38.15	$38.20
Purchase #3	$92.33	13.837%	$105.1057	$105.11	$105.10	$105.10
Purchase #4	$13.61	13.404%	$15.4343	$15.43	$15.45	$15.40
Purchase #5	$120.80	13.169%	$136.7082	$136.71	$136.70	$136.70
Purchase #6	$154.60	12.272%	$173.5725	$173.57	$173.55	$173.60
Purchase #7	$102.40	5.256%	$107.7821	$107.78	$107.80	$107.80
7 purchase totals =	$587.59		$654.8748	$654.87	$654.85	$654.90