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	$81.33	10.849%	$90.1535	$90.15	$90.15	$90.20
Purchase #2	$231.74	9.290%	$253.2686	$253.27	$253.25	$253.30
Purchase #3	$73.48	4.311%	$76.6477	$76.65	$76.65	$76.60
Purchase #4	$168.59	5.612%	$178.0513	$178.05	$178.05	$178.10
Purchase #5	$97.27	6.285%	$103.3834	$103.38	$103.40	$103.40
Purchase #6	$49.38	4.552%	$51.6278	$51.63	$51.65	$51.60
Purchase #7	$136.48	12.465%	$153.4922	$153.49	$153.50	$153.50
7 purchase totals =	$838.27		$906.6245	$906.62	$906.65	$906.70