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	$86.89	3.745%	$90.144	$90.14	$90.15	$90.10
Purchase #2	$155.30	10.103%	$170.99	$170.99	$171.00	$171.00
Purchase #3	$232.63	9.830%	$255.4975	$255.50	$255.50	$255.50
Purchase #4	$168.85	12.854%	$190.554	$190.55	$190.55	$190.60
Purchase #5	$104.75	6.659%	$111.7253	$111.73	$111.75	$111.70
Purchase #6	$226.38	7.338%	$242.9918	$242.99	$243.00	$243.00
Purchase #7	$67.65	9.600%	$74.1444	$74.14	$74.15	$74.10
7 purchase totals =	$1,042.45		$1,136.0470	$1,136.04	$1,136.10	$1,136.00