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	$90.85	9.651%	$99.6179	$99.62	$99.60	$99.60
Purchase #2	$175.79	9.209%	$191.9785	$191.98	$192.00	$192.00
Purchase #3	$177.46	11.224%	$197.3781	$197.38	$197.40	$197.40
Purchase #4	$45.81	10.302%	$50.5293	$50.53	$50.55	$50.50
Purchase #5	$91.76	3.697%	$95.1524	$95.15	$95.15	$95.20
Purchase #6	$80.98	13.274%	$91.7293	$91.73	$91.75	$91.70
Purchase #7	$164.54	4.432%	$171.8324	$171.83	$171.85	$171.80
7 purchase totals =	$827.19		$898.2179	$898.22	$898.30	$898.20