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	$52.66	6.521%	$56.094	$56.09	$56.10	$56.10
Purchase #2	$227.56	6.290%	$241.8735	$241.87	$241.85	$241.90
Purchase #3	$111.34	6.398%	$118.4635	$118.46	$118.45	$118.50
Purchase #4	$98.30	7.563%	$105.7344	$105.73	$105.75	$105.70
Purchase #5	$226.50	8.159%	$244.9801	$244.98	$245.00	$245.00
Purchase #6	$243.94	7.346%	$261.8598	$261.86	$261.85	$261.90
Purchase #7	$118.47	10.649%	$131.0859	$131.09	$131.10	$131.10
7 purchase totals =	$1,078.77		$1,160.0912	$1,160.08	$1,160.10	$1,160.20