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	$91.91	9.816%	$100.9319	$100.93	$100.95	$100.90
Purchase #2	$169.55	5.286%	$178.5124	$178.51	$178.50	$178.50
Purchase #3	$243.60	7.657%	$262.2525	$262.25	$262.25	$262.30
Purchase #4	$133.78	5.716%	$141.4269	$141.43	$141.45	$141.40
Purchase #5	$115.33	6.253%	$122.5416	$122.54	$122.55	$122.50
Purchase #6	$46.60	8.734%	$50.67	$50.67	$50.65	$50.70
Purchase #7	$75.44	12.854%	$85.1371	$85.14	$85.15	$85.10
7 purchase totals =	$876.21		$941.4724	$941.47	$941.50	$941.40