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	$108.69	11.614%	$121.3133	$121.31	$121.30	$121.30
Purchase #2	$171.81	5.112%	$180.5929	$180.59	$180.60	$180.60
Purchase #3	$83.57	8.622%	$90.7754	$90.78	$90.80	$90.80
Purchase #4	$154.60	4.677%	$161.8306	$161.83	$161.85	$161.80
Purchase #5	$152.82	3.828%	$158.6699	$158.67	$158.65	$158.70
Purchase #6	$77.70	6.596%	$82.8251	$82.83	$82.85	$82.80
Purchase #7	$74.97	9.621%	$82.1829	$82.18	$82.20	$82.20
7 purchase totals =	$824.16		$878.1901	$878.19	$878.25	$878.20