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	$118.61	10.443%	$130.9964	$131.00	$131.00	$131.00
Purchase #2	$57.29	12.730%	$64.583	$64.58	$64.60	$64.60
Purchase #3	$206.92	13.765%	$235.4025	$235.40	$235.40	$235.40
Purchase #4	$95.82	9.702%	$105.1165	$105.12	$105.10	$105.10
Purchase #5	$238.89	8.347%	$258.8301	$258.83	$258.85	$258.80
Purchase #6	$50.58	3.354%	$52.2765	$52.28	$52.30	$52.30
Purchase #7	$136.42	3.576%	$141.2984	$141.30	$141.30	$141.30
7 purchase totals =	$904.53		$988.5034	$988.51	$988.55	$988.50