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	$105.86	9.126%	$115.5208	$115.52	$115.50	$115.50
Purchase #2	$48.93	6.344%	$52.0341	$52.03	$52.05	$52.00
Purchase #3	$39.87	5.542%	$42.0796	$42.08	$42.10	$42.10
Purchase #4	$155.35	10.175%	$171.1569	$171.16	$171.15	$171.20
Purchase #5	$75.27	10.302%	$83.0243	$83.02	$83.00	$83.00
Purchase #6	$75.28	7.113%	$80.6347	$80.63	$80.65	$80.60
Purchase #7	$79.81	11.716%	$89.1605	$89.16	$89.15	$89.20
7 purchase totals =	$580.37		$633.6109	$633.60	$633.60	$633.60