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	$7.61	9.168%	$8.3077	$8.31	$8.30	$8.30
Purchase #2	$95.25	9.163%	$103.9778	$103.98	$104.00	$104.00
Purchase #3	$42.62	11.231%	$47.4067	$47.41	$47.40	$47.40
Purchase #4	$81.33	10.321%	$89.7241	$89.72	$89.70	$89.70
Purchase #5	$95.72	5.261%	$100.7558	$100.76	$100.75	$100.80
Purchase #6	$98.68	10.254%	$108.7986	$108.80	$108.80	$108.80
Purchase #7	$19.51	6.801%	$20.8369	$20.84	$20.85	$20.80
7 purchase totals =	$440.72		$479.8076	$479.82	$479.80	$479.80