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	$79.55	13.563%	$90.3394	$90.34	$90.35	$90.30
Purchase #2	$104.87	11.691%	$117.1304	$117.13	$117.15	$117.10
Purchase #3	$245.87	11.400%	$273.8992	$273.90	$273.90	$273.90
Purchase #4	$57.69	8.686%	$62.701	$62.70	$62.70	$62.70
Purchase #5	$173.97	9.861%	$191.1252	$191.13	$191.15	$191.10
Purchase #6	$82.80	11.812%	$92.5803	$92.58	$92.60	$92.60
Purchase #7	$53.39	8.137%	$57.7343	$57.73	$57.75	$57.70
7 purchase totals =	$798.14		$885.5098	$885.51	$885.60	$885.40