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	$225.67	13.322%	$255.7338	$255.73	$255.75	$255.70
Purchase #2	$50.76	8.505%	$55.0771	$55.08	$55.10	$55.10
Purchase #3	$28.85	13.212%	$32.6617	$32.66	$32.65	$32.70
Purchase #4	$167.34	10.542%	$184.981	$184.98	$185.00	$185.00
Purchase #5	$93.98	12.613%	$105.8337	$105.83	$105.85	$105.80
Purchase #6	$48.42	8.259%	$52.419	$52.42	$52.40	$52.40
Purchase #7	$161.35	10.818%	$178.8048	$178.80	$178.80	$178.80
7 purchase totals =	$776.37		$865.5111	$865.50	$865.55	$865.50