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	$244.88	9.615%	$268.4252	$268.43	$268.45	$268.40
Purchase #2	$38.65	10.556%	$42.7299	$42.73	$42.75	$42.70
Purchase #3	$92.78	7.851%	$100.0642	$100.06	$100.05	$100.10
Purchase #4	$116.98	3.689%	$121.2954	$121.30	$121.30	$121.30
Purchase #5	$68.79	5.684%	$72.7	$72.70	$72.70	$72.70
Purchase #6	$96.96	7.119%	$103.8626	$103.86	$103.85	$103.90
Purchase #7	$116.26	9.661%	$127.4919	$127.49	$127.50	$127.50
7 purchase totals =	$775.30		$836.5692	$836.57	$836.60	$836.60