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	$116.96	5.828%	$123.7764	$123.78	$123.80	$123.80
Purchase #2	$49.48	9.834%	$54.3459	$54.35	$54.35	$54.30
Purchase #3	$92.80	8.205%	$100.4142	$100.41	$100.40	$100.40
Purchase #4	$59.67	5.791%	$63.1255	$63.13	$63.15	$63.10
Purchase #5	$21.56	8.426%	$23.3766	$23.38	$23.40	$23.40
Purchase #6	$68.53	5.715%	$72.4465	$72.45	$72.45	$72.40
Purchase #7	$106.92	9.551%	$117.1319	$117.13	$117.15	$117.10
7 purchase totals =	$515.92		$554.6170	$554.63	$554.70	$554.50