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	$78.32	10.549%	$86.582	$86.58	$86.60	$86.60
Purchase #2	$80.82	12.457%	$90.8877	$90.89	$90.90	$90.90
Purchase #3	$77.86	9.487%	$85.2466	$85.25	$85.25	$85.20
Purchase #4	$166.26	10.666%	$183.9933	$183.99	$184.00	$184.00
Purchase #5	$19.72	13.376%	$22.3577	$22.36	$22.35	$22.40
Purchase #6	$27.42	13.419%	$31.0995	$31.10	$31.10	$31.10
Purchase #7	$48.94	4.774%	$51.2764	$51.28	$51.30	$51.30
7 purchase totals =	$499.34		$551.4432	$551.45	$551.50	$551.50