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	$219.76	13.372%	$249.1463	$249.15	$249.15	$249.10
Purchase #2	$31.32	10.550%	$34.6243	$34.62	$34.60	$34.60
Purchase #3	$100.90	12.261%	$113.2713	$113.27	$113.25	$113.30
Purchase #4	$89.82	11.852%	$100.4655	$100.47	$100.45	$100.50
Purchase #5	$189.96	5.580%	$200.5598	$200.56	$200.55	$200.60
Purchase #6	$53.63	10.687%	$59.3614	$59.36	$59.35	$59.40
Purchase #7	$103.86	9.354%	$113.5751	$113.58	$113.60	$113.60
7 purchase totals =	$789.25		$871.0037	$871.01	$870.95	$871.10