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	$72.67	10.744%	$80.4777	$80.48	$80.50	$80.50
Purchase #2	$60.31	13.649%	$68.5417	$68.54	$68.55	$68.50
Purchase #3	$166.38	9.775%	$182.6436	$182.64	$182.65	$182.60
Purchase #4	$242.56	3.244%	$250.4286	$250.43	$250.45	$250.40
Purchase #5	$172.78	10.344%	$190.6524	$190.65	$190.65	$190.70
Purchase #6	$240.67	9.180%	$262.7635	$262.76	$262.75	$262.80
Purchase #7	$204.63	7.451%	$219.877	$219.88	$219.90	$219.90
7 purchase totals =	$1,160.00		$1,255.3845	$1,255.38	$1,255.45	$1,255.40