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	$47.72	10.121%	$52.5497	$52.55	$52.55	$52.50
Purchase #2	$215.53	7.193%	$231.0331	$231.03	$231.05	$231.00
Purchase #3	$96.27	4.193%	$100.3066	$100.31	$100.30	$100.30
Purchase #4	$134.80	9.845%	$148.0711	$148.07	$148.05	$148.10
Purchase #5	$114.27	7.764%	$123.1419	$123.14	$123.15	$123.10
Purchase #6	$130.91	5.852%	$138.5709	$138.57	$138.55	$138.60
Purchase #7	$83.39	3.455%	$86.2711	$86.27	$86.25	$86.30
7 purchase totals =	$822.89		$879.9444	$879.94	$879.90	$879.90