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	$180.86	10.676%	$200.1686	$200.17	$200.15	$200.20
Purchase #2	$27.53	6.392%	$29.2897	$29.29	$29.30	$29.30
Purchase #3	$22.44	9.733%	$24.6241	$24.62	$24.60	$24.60
Purchase #4	$67.49	6.865%	$72.1232	$72.12	$72.10	$72.10
Purchase #5	$208.43	3.402%	$215.5208	$215.52	$215.50	$215.50
Purchase #6	$80.93	9.355%	$88.501	$88.50	$88.50	$88.50
Purchase #7	$161.42	4.127%	$168.0818	$168.08	$168.10	$168.10
7 purchase totals =	$749.10		$798.3092	$798.30	$798.25	$798.30