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	$101.49	7.503%	$109.1048	$109.10	$109.10	$109.10
Purchase #2	$63.82	10.589%	$70.5779	$70.58	$70.60	$70.60
Purchase #3	$103.95	3.351%	$107.4334	$107.43	$107.45	$107.40
Purchase #4	$249.33	3.364%	$257.7175	$257.72	$257.70	$257.70
Purchase #5	$243.40	4.303%	$253.8735	$253.87	$253.85	$253.90
Purchase #6	$37.78	7.151%	$40.4816	$40.48	$40.50	$40.50
Purchase #7	$216.63	6.839%	$231.4453	$231.45	$231.45	$231.40
7 purchase totals =	$1,016.40		$1,070.6340	$1,070.63	$1,070.65	$1,070.60