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	$81.76	8.620%	$88.8077	$88.81	$88.80	$88.80
Purchase #2	$243.49	12.720%	$274.4619	$274.46	$274.45	$274.50
Purchase #3	$191.77	10.375%	$211.6661	$211.67	$211.65	$211.70
Purchase #4	$95.25	9.130%	$103.9463	$103.95	$103.95	$103.90
Purchase #5	$71.54	9.238%	$78.1489	$78.15	$78.15	$78.10
Purchase #6	$29.63	3.268%	$30.5983	$30.60	$30.60	$30.60
Purchase #7	$249.80	3.228%	$257.8635	$257.86	$257.85	$257.90
7 purchase totals =	$963.24		$1,045.4927	$1,045.50	$1,045.45	$1,045.50