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	$84.39	11.784%	$94.3345	$94.33	$94.35	$94.30
Purchase #2	$94.35	5.255%	$99.3081	$99.31	$99.30	$99.30
Purchase #3	$187.68	11.632%	$209.5109	$209.51	$209.50	$209.50
Purchase #4	$172.82	7.864%	$186.4106	$186.41	$186.40	$186.40
Purchase #5	$238.81	5.777%	$252.6061	$252.61	$252.60	$252.60
Purchase #6	$143.85	8.785%	$156.4872	$156.49	$156.50	$156.50
Purchase #7	$91.31	10.436%	$100.8391	$100.84	$100.85	$100.80
7 purchase totals =	$1,013.21		$1,099.4965	$1,099.50	$1,099.50	$1,099.40