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	$71.87	9.294%	$78.5496	$78.55	$78.55	$78.50
Purchase #2	$204.28	5.154%	$214.8086	$214.81	$214.80	$214.80
Purchase #3	$73.70	12.227%	$82.7113	$82.71	$82.70	$82.70
Purchase #4	$249.54	3.454%	$258.1591	$258.16	$258.15	$258.20
Purchase #5	$35.61	13.865%	$40.5473	$40.55	$40.55	$40.50
Purchase #6	$212.89	13.380%	$241.3747	$241.37	$241.35	$241.40
Purchase #7	$211.28	7.253%	$226.6041	$226.60	$226.60	$226.60
7 purchase totals =	$1,059.17		$1,142.7547	$1,142.75	$1,142.70	$1,142.70