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	$90.86	8.432%	$98.5213	$98.52	$98.50	$98.50
Purchase #2	$70.32	10.636%	$77.7992	$77.80	$77.80	$77.80
Purchase #3	$56.74	4.673%	$59.3915	$59.39	$59.40	$59.40
Purchase #4	$180.89	7.478%	$194.417	$194.42	$194.40	$194.40
Purchase #5	$222.66	4.115%	$231.8225	$231.82	$231.80	$231.80
Purchase #6	$58.37	3.362%	$60.3324	$60.33	$60.35	$60.30
Purchase #7	$109.94	10.713%	$121.7179	$121.72	$121.70	$121.70
7 purchase totals =	$789.78		$844.0018	$844.00	$843.95	$843.90