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	$103.82	5.170%	$109.1875	$109.19	$109.20	$109.20
Purchase #2	$164.64	9.338%	$180.0141	$180.01	$180.00	$180.00
Purchase #3	$197.62	9.867%	$217.1192	$217.12	$217.10	$217.10
Purchase #4	$15.38	13.695%	$17.4863	$17.49	$17.50	$17.50
Purchase #5	$248.68	7.155%	$266.4731	$266.47	$266.45	$266.50
Purchase #6	$180.51	13.495%	$204.8698	$204.87	$204.85	$204.90
Purchase #7	$96.89	8.392%	$105.021	$105.02	$105.00	$105.00
7 purchase totals =	$1,007.54		$1,100.1710	$1,100.17	$1,100.10	$1,100.20