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	$47.71	6.415%	$50.7706	$50.77	$50.75	$50.80
Purchase #2	$76.69	4.348%	$80.0245	$80.02	$80.00	$80.00
Purchase #3	$106.83	8.819%	$116.2513	$116.25	$116.25	$116.30
Purchase #4	$30.45	8.869%	$33.1506	$33.15	$33.15	$33.20
Purchase #5	$27.66	4.301%	$28.8497	$28.85	$28.85	$28.80
Purchase #6	$114.52	8.152%	$123.8557	$123.86	$123.85	$123.90
Purchase #7	$25.97	10.372%	$28.6636	$28.66	$28.65	$28.70
7 purchase totals =	$429.83		$461.5660	$461.56	$461.50	$461.70