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	$90.25	5.654%	$95.3527	$95.35	$95.35	$95.40
Purchase #2	$184.63	13.457%	$209.4757	$209.48	$209.50	$209.50
Purchase #3	$231.35	12.289%	$259.7806	$259.78	$259.80	$259.80
Purchase #4	$19.58	3.776%	$20.3193	$20.32	$20.30	$20.30
Purchase #5	$137.60	12.766%	$155.166	$155.17	$155.15	$155.20
Purchase #6	$73.90	8.572%	$80.2347	$80.23	$80.25	$80.20
Purchase #7	$150.88	11.659%	$168.4711	$168.47	$168.45	$168.50
7 purchase totals =	$888.19		$988.8001	$988.80	$988.80	$988.90