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	$82.80	8.727%	$90.026	$90.03	$90.05	$90.00
Purchase #2	$44.96	8.453%	$48.7605	$48.76	$48.75	$48.80
Purchase #3	$127.47	13.502%	$144.681	$144.68	$144.70	$144.70
Purchase #4	$188.64	6.411%	$200.7337	$200.73	$200.75	$200.70
Purchase #5	$144.66	13.822%	$164.6549	$164.65	$164.65	$164.70
Purchase #6	$243.25	7.107%	$260.5378	$260.54	$260.55	$260.50
Purchase #7	$19.45	11.509%	$21.6885	$21.69	$21.70	$21.70
7 purchase totals =	$851.23		$931.0824	$931.08	$931.15	$931.10