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	$165.68	8.668%	$180.0411	$180.04	$180.05	$180.00
Purchase #2	$146.41	12.542%	$164.7727	$164.77	$164.75	$164.80
Purchase #3	$25.79	7.214%	$27.6505	$27.65	$27.65	$27.70
Purchase #4	$150.40	7.760%	$162.071	$162.07	$162.05	$162.10
Purchase #5	$151.71	9.704%	$166.4319	$166.43	$166.45	$166.40
Purchase #6	$90.75	13.845%	$103.3143	$103.31	$103.30	$103.30
Purchase #7	$247.66	3.850%	$257.1949	$257.19	$257.20	$257.20
7 purchase totals =	$978.40		$1,061.4764	$1,061.46	$1,061.45	$1,061.50