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	$54.47	7.314%	$58.4539	$58.45	$58.45	$58.50
Purchase #2	$145.58	7.747%	$156.8581	$156.86	$156.85	$156.90
Purchase #3	$20.97	12.209%	$23.5302	$23.53	$23.55	$23.50
Purchase #4	$18.64	11.245%	$20.7361	$20.74	$20.75	$20.70
Purchase #5	$67.59	7.164%	$72.4321	$72.43	$72.45	$72.40
Purchase #6	$174.67	8.146%	$188.8986	$188.90	$188.90	$188.90
Purchase #7	$77.66	3.520%	$80.3936	$80.39	$80.40	$80.40
7 purchase totals =	$559.58		$601.3026	$601.30	$601.35	$601.30