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	$75.68	8.867%	$82.3905	$82.39	$82.40	$82.40
Purchase #2	$143.26	3.688%	$148.5434	$148.54	$148.55	$148.50
Purchase #3	$204.28	11.391%	$227.5495	$227.55	$227.55	$227.50
Purchase #4	$104.83	7.836%	$113.0445	$113.04	$113.05	$113.00
Purchase #5	$95.73	8.315%	$103.6899	$103.69	$103.70	$103.70
Purchase #6	$81.85	4.478%	$85.5152	$85.52	$85.50	$85.50
Purchase #7	$20.62	10.840%	$22.8552	$22.86	$22.85	$22.90
7 purchase totals =	$726.25		$783.5882	$783.59	$783.60	$783.50