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	$224.72	10.144%	$247.5156	$247.52	$247.50	$247.50
Purchase #2	$138.65	10.203%	$152.7965	$152.80	$152.80	$152.80
Purchase #3	$127.54	10.175%	$140.5172	$140.52	$140.50	$140.50
Purchase #4	$249.81	11.646%	$278.9029	$278.90	$278.90	$278.90
Purchase #5	$96.90	5.361%	$102.0948	$102.09	$102.10	$102.10
Purchase #6	$105.58	6.814%	$112.7742	$112.77	$112.75	$112.80
Purchase #7	$244.27	10.373%	$269.6081	$269.61	$269.60	$269.60
7 purchase totals =	$1,187.47		$1,304.2093	$1,304.21	$1,304.15	$1,304.20