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	$50.69	11.714%	$56.6278	$56.63	$56.65	$56.60
Purchase #2	$125.80	3.359%	$130.0256	$130.03	$130.05	$130.00
Purchase #3	$71.82	8.536%	$77.9506	$77.95	$77.95	$78.00
Purchase #4	$76.53	5.295%	$80.5823	$80.58	$80.60	$80.60
Purchase #5	$168.72	11.154%	$187.539	$187.54	$187.55	$187.50
Purchase #6	$178.58	4.143%	$185.9786	$185.98	$186.00	$186.00
Purchase #7	$96.82	8.250%	$104.8077	$104.81	$104.80	$104.80
7 purchase totals =	$768.96		$823.5116	$823.52	$823.60	$823.50