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	$138.50	8.584%	$150.3888	$150.39	$150.40	$150.40
Purchase #2	$20.38	3.263%	$21.045	$21.05	$21.05	$21.00
Purchase #3	$50.38	6.480%	$53.6446	$53.64	$53.65	$53.60
Purchase #4	$162.99	5.819%	$172.4744	$172.47	$172.45	$172.50
Purchase #5	$97.35	12.409%	$109.4302	$109.43	$109.45	$109.40
Purchase #6	$183.91	10.585%	$203.3769	$203.38	$203.40	$203.40
Purchase #7	$220.60	11.480%	$245.9249	$245.92	$245.90	$245.90
7 purchase totals =	$874.11		$956.2848	$956.28	$956.30	$956.20