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	$112.73	6.535%	$120.0969	$120.10	$120.10	$120.10
Purchase #2	$118.96	6.756%	$126.9969	$127.00	$127.00	$127.00
Purchase #3	$95.45	8.244%	$103.3189	$103.32	$103.30	$103.30
Purchase #4	$82.64	13.268%	$93.6047	$93.60	$93.60	$93.60
Purchase #5	$26.35	8.551%	$28.6032	$28.60	$28.60	$28.60
Purchase #6	$50.83	5.259%	$53.5031	$53.50	$53.50	$53.50
Purchase #7	$219.43	9.504%	$240.2846	$240.28	$240.30	$240.30
7 purchase totals =	$706.39		$766.4083	$766.40	$766.40	$766.40