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	$57.38	3.559%	$59.4222	$59.42	$59.40	$59.40
Purchase #2	$188.84	10.838%	$209.3065	$209.31	$209.30	$209.30
Purchase #3	$219.82	8.112%	$237.6518	$237.65	$237.65	$237.70
Purchase #4	$127.27	12.339%	$142.9738	$142.97	$142.95	$143.00
Purchase #5	$19.29	13.764%	$21.9451	$21.95	$21.95	$21.90
Purchase #6	$139.90	8.293%	$151.5019	$151.50	$151.50	$151.50
Purchase #7	$87.50	6.807%	$93.4561	$93.46	$93.45	$93.50
7 purchase totals =	$840.00		$916.2574	$916.26	$916.20	$916.30