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	$26.60	9.515%	$29.131	$29.13	$29.15	$29.10
Purchase #2	$71.83	10.559%	$79.4145	$79.41	$79.40	$79.40
Purchase #3	$205.91	6.601%	$219.5021	$219.50	$219.50	$219.50
Purchase #4	$133.42	4.675%	$139.6574	$139.66	$139.65	$139.70
Purchase #5	$78.42	5.531%	$82.7574	$82.76	$82.75	$82.80
Purchase #6	$90.57	12.313%	$101.7219	$101.72	$101.70	$101.70
Purchase #7	$221.70	5.302%	$233.4545	$233.45	$233.45	$233.50
7 purchase totals =	$828.45		$885.6388	$885.63	$885.60	$885.70