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	$26.39	12.289%	$29.6331	$29.63	$29.65	$29.60
Purchase #2	$63.76	12.460%	$71.7045	$71.70	$71.70	$71.70
Purchase #3	$67.28	4.538%	$70.3332	$70.33	$70.35	$70.30
Purchase #4	$188.89	10.788%	$209.2675	$209.27	$209.25	$209.30
Purchase #5	$121.87	4.581%	$127.4529	$127.45	$127.45	$127.50
Purchase #6	$247.77	3.295%	$255.934	$255.93	$255.95	$255.90
Purchase #7	$172.42	7.608%	$185.5377	$185.54	$185.55	$185.50
7 purchase totals =	$888.38		$949.8629	$949.85	$949.90	$949.80