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	$48.73	11.367%	$54.2691	$54.27	$54.25	$54.30
Purchase #2	$145.27	4.654%	$152.0309	$152.03	$152.05	$152.00
Purchase #3	$24.25	11.369%	$27.007	$27.01	$27.00	$27.00
Purchase #4	$120.96	10.343%	$133.4709	$133.47	$133.45	$133.50
Purchase #5	$93.86	13.421%	$106.457	$106.46	$106.45	$106.50
Purchase #6	$48.37	4.136%	$50.3706	$50.37	$50.35	$50.40
Purchase #7	$12.81	8.609%	$13.9128	$13.91	$13.90	$13.90
7 purchase totals =	$494.25		$537.5183	$537.52	$537.45	$537.60