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	$100.76	5.589%	$106.3915	$106.39	$106.40	$106.40
Purchase #2	$118.82	10.652%	$131.4767	$131.48	$131.50	$131.50
Purchase #3	$117.41	13.264%	$132.9833	$132.98	$133.00	$133.00
Purchase #4	$96.42	12.306%	$108.2854	$108.29	$108.30	$108.30
Purchase #5	$218.87	11.671%	$244.4143	$244.41	$244.40	$244.40
Purchase #6	$54.42	10.528%	$60.1493	$60.15	$60.15	$60.10
Purchase #7	$82.52	3.510%	$85.4165	$85.42	$85.40	$85.40
7 purchase totals =	$789.22		$869.1170	$869.12	$869.15	$869.10