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	$204.78	6.643%	$218.3835	$218.38	$218.40	$218.40
Purchase #2	$110.54	3.820%	$114.7626	$114.76	$114.75	$114.80
Purchase #3	$184.67	10.262%	$203.6208	$203.62	$203.60	$203.60
Purchase #4	$248.76	13.378%	$282.0391	$282.04	$282.05	$282.00
Purchase #5	$18.25	11.360%	$20.3232	$20.32	$20.30	$20.30
Purchase #6	$119.43	3.570%	$123.6937	$123.69	$123.70	$123.70
Purchase #7	$136.71	12.417%	$153.6853	$153.69	$153.70	$153.70
7 purchase totals =	$1,023.14		$1,116.5082	$1,116.50	$1,116.50	$1,116.50