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	$72.74	7.434%	$78.1475	$78.15	$78.15	$78.10
Purchase #2	$133.27	12.749%	$150.2606	$150.26	$150.25	$150.30
Purchase #3	$149.74	9.269%	$163.6194	$163.62	$163.60	$163.60
Purchase #4	$249.56	8.407%	$270.5405	$270.54	$270.55	$270.50
Purchase #5	$20.62	13.785%	$23.4625	$23.46	$23.45	$23.50
Purchase #6	$103.98	7.263%	$111.5321	$111.53	$111.55	$111.50
Purchase #7	$207.25	12.852%	$233.8858	$233.89	$233.90	$233.90
7 purchase totals =	$937.16		$1,031.4484	$1,031.45	$1,031.45	$1,031.40