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	$247.29	8.834%	$269.1356	$269.14	$269.15	$269.10
Purchase #2	$141.33	12.455%	$158.9327	$158.93	$158.95	$158.90
Purchase #3	$105.38	10.655%	$116.6082	$116.61	$116.60	$116.60
Purchase #4	$43.38	12.829%	$48.9452	$48.95	$48.95	$48.90
Purchase #5	$6.85	13.165%	$7.7518	$7.75	$7.75	$7.80
Purchase #6	$151.94	9.835%	$166.8833	$166.88	$166.90	$166.90
Purchase #7	$29.42	11.632%	$32.8421	$32.84	$32.85	$32.80
7 purchase totals =	$725.59		$801.0989	$801.10	$801.15	$801.00