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	$47.87	10.390%	$52.8437	$52.84	$52.85	$52.80
Purchase #2	$99.39	4.501%	$103.8635	$103.86	$103.85	$103.90
Purchase #3	$236.52	12.596%	$266.3121	$266.31	$266.30	$266.30
Purchase #4	$133.88	13.154%	$151.4906	$151.49	$151.50	$151.50
Purchase #5	$66.33	13.642%	$75.3787	$75.38	$75.40	$75.40
Purchase #6	$84.53	13.435%	$95.8866	$95.89	$95.90	$95.90
Purchase #7	$83.77	3.833%	$86.9809	$86.98	$87.00	$87.00
7 purchase totals =	$752.29		$832.7561	$832.75	$832.80	$832.80