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	$66.85	8.458%	$72.5042	$72.50	$72.50	$72.50
Purchase #2	$121.50	10.625%	$134.4094	$134.41	$134.40	$134.40
Purchase #3	$147.72	5.675%	$156.1031	$156.10	$156.10	$156.10
Purchase #4	$174.40	9.103%	$190.2756	$190.28	$190.30	$190.30
Purchase #5	$51.33	6.733%	$54.786	$54.79	$54.80	$54.80
Purchase #6	$84.99	10.393%	$93.823	$93.82	$93.80	$93.80
Purchase #7	$174.64	9.653%	$191.498	$191.50	$191.50	$191.50
7 purchase totals =	$821.43		$893.3993	$893.40	$893.40	$893.40