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	$81.64	9.494%	$89.3909	$89.39	$89.40	$89.40
Purchase #2	$37.98	4.268%	$39.601	$39.60	$39.60	$39.60
Purchase #3	$53.56	11.380%	$59.6551	$59.66	$59.65	$59.70
Purchase #4	$147.68	5.271%	$155.4642	$155.46	$155.45	$155.50
Purchase #5	$81.58	6.499%	$86.8819	$86.88	$86.90	$86.90
Purchase #6	$20.99	4.366%	$21.9064	$21.91	$21.90	$21.90
Purchase #7	$100.37	5.159%	$105.5481	$105.55	$105.55	$105.50
7 purchase totals =	$523.80		$558.4476	$558.45	$558.45	$558.50