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	$105.91	12.329%	$118.9676	$118.97	$118.95	$119.00
Purchase #2	$111.61	10.388%	$123.204	$123.20	$123.20	$123.20
Purchase #3	$125.30	12.391%	$140.8259	$140.83	$140.85	$140.80
Purchase #4	$115.28	10.674%	$127.585	$127.59	$127.60	$127.60
Purchase #5	$106.72	11.621%	$119.1219	$119.12	$119.10	$119.10
Purchase #6	$82.25	6.520%	$87.6127	$87.61	$87.60	$87.60
Purchase #7	$243.43	9.437%	$266.4025	$266.40	$266.40	$266.40
7 purchase totals =	$890.50		$983.7196	$983.72	$983.70	$983.70