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	$82.98	8.195%	$89.7802	$89.78	$89.80	$89.80
Purchase #2	$133.81	11.553%	$149.2691	$149.27	$149.25	$149.30
Purchase #3	$88.36	7.342%	$94.8474	$94.85	$94.85	$94.80
Purchase #4	$74.64	5.351%	$78.634	$78.63	$78.65	$78.60
Purchase #5	$129.60	11.835%	$144.9382	$144.94	$144.95	$144.90
Purchase #6	$103.78	10.599%	$114.7796	$114.78	$114.80	$114.80
Purchase #7	$192.66	8.681%	$209.3848	$209.38	$209.40	$209.40
7 purchase totals =	$805.83		$881.6333	$881.63	$881.70	$881.60