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	$217.44	13.873%	$247.6055	$247.61	$247.60	$247.60
Purchase #2	$151.86	10.655%	$168.0407	$168.04	$168.05	$168.00
Purchase #3	$62.69	5.170%	$65.9311	$65.93	$65.95	$65.90
Purchase #4	$8.41	5.815%	$8.899	$8.90	$8.90	$8.90
Purchase #5	$93.61	6.721%	$99.9015	$99.90	$99.90	$99.90
Purchase #6	$106.78	9.833%	$117.2797	$117.28	$117.30	$117.30
Purchase #7	$84.52	10.584%	$93.4656	$93.47	$93.45	$93.50
7 purchase totals =	$725.31		$801.1231	$801.13	$801.15	$801.10