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	$150.99	13.443%	$171.2876	$171.29	$171.30	$171.30
Purchase #2	$106.57	10.359%	$117.6096	$117.61	$117.60	$117.60
Purchase #3	$204.43	10.572%	$226.0423	$226.04	$226.05	$226.00
Purchase #4	$184.48	5.474%	$194.5784	$194.58	$194.60	$194.60
Purchase #5	$97.60	11.308%	$108.6366	$108.64	$108.65	$108.60
Purchase #6	$91.89	12.348%	$103.2366	$103.24	$103.25	$103.20
Purchase #7	$52.34	8.674%	$56.88	$56.88	$56.90	$56.90
7 purchase totals =	$888.30		$978.2711	$978.28	$978.35	$978.20