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	$116.49	9.452%	$127.5006	$127.50	$127.50	$127.50
Purchase #2	$154.79	3.430%	$160.0993	$160.10	$160.10	$160.10
Purchase #3	$86.91	4.302%	$90.6489	$90.65	$90.65	$90.60
Purchase #4	$166.75	7.230%	$178.806	$178.81	$178.80	$178.80
Purchase #5	$77.71	8.448%	$84.2749	$84.27	$84.25	$84.30
Purchase #6	$162.92	13.126%	$184.3049	$184.30	$184.30	$184.30
Purchase #7	$139.98	9.282%	$152.9729	$152.97	$152.95	$153.00
7 purchase totals =	$905.55		$978.6075	$978.60	$978.55	$978.60