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	$70.96	9.587%	$77.7629	$77.76	$77.75	$77.80
Purchase #2	$101.59	6.392%	$108.0836	$108.08	$108.10	$108.10
Purchase #3	$6.27	4.415%	$6.5468	$6.55	$6.55	$6.50
Purchase #4	$29.90	12.187%	$33.5439	$33.54	$33.55	$33.50
Purchase #5	$50.62	8.495%	$54.9202	$54.92	$54.90	$54.90
Purchase #6	$67.88	6.549%	$72.3255	$72.33	$72.35	$72.30
Purchase #7	$140.72	5.643%	$148.6608	$148.66	$148.65	$148.70
7 purchase totals =	$467.94		$501.8437	$501.84	$501.85	$501.80