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	$80.98	10.795%	$89.7218	$89.72	$89.70	$89.70
Purchase #2	$158.27	13.838%	$180.1714	$180.17	$180.15	$180.20
Purchase #3	$91.45	11.696%	$102.146	$102.15	$102.15	$102.10
Purchase #4	$151.63	3.188%	$156.464	$156.46	$156.45	$156.50
Purchase #5	$28.41	5.377%	$29.9376	$29.94	$29.95	$29.90
Purchase #6	$180.80	13.787%	$205.7269	$205.73	$205.75	$205.70
Purchase #7	$215.57	12.467%	$242.4451	$242.45	$242.45	$242.40
7 purchase totals =	$907.11		$1,006.6128	$1,006.62	$1,006.60	$1,006.50