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	$28.92	10.576%	$31.9786	$31.98	$32.00	$32.00
Purchase #2	$145.35	6.633%	$154.9911	$154.99	$155.00	$155.00
Purchase #3	$20.42	5.677%	$21.5792	$21.58	$21.60	$21.60
Purchase #4	$100.51	13.706%	$114.2859	$114.29	$114.30	$114.30
Purchase #5	$145.89	4.380%	$152.28	$152.28	$152.30	$152.30
Purchase #6	$148.69	11.465%	$165.7373	$165.74	$165.75	$165.70
Purchase #7	$45.98	4.355%	$47.9824	$47.98	$48.00	$48.00
7 purchase totals =	$635.76		$688.8345	$688.84	$688.95	$688.90