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	$240.94	10.461%	$266.1447	$266.14	$266.15	$266.10
Purchase #2	$99.50	3.816%	$103.2969	$103.30	$103.30	$103.30
Purchase #3	$95.27	4.307%	$99.3733	$99.37	$99.35	$99.40
Purchase #4	$249.89	10.669%	$276.5508	$276.55	$276.55	$276.60
Purchase #5	$119.29	10.239%	$131.5041	$131.50	$131.50	$131.50
Purchase #6	$50.31	11.814%	$56.2536	$56.25	$56.25	$56.30
Purchase #7	$235.67	8.279%	$255.1811	$255.18	$255.20	$255.20
7 purchase totals =	$1,090.87		$1,188.3045	$1,188.29	$1,188.30	$1,188.40