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	$83.33	10.470%	$92.0547	$92.05	$92.05	$92.10
Purchase #2	$100.81	5.660%	$106.5158	$106.52	$106.50	$106.50
Purchase #3	$78.38	10.275%	$86.4335	$86.43	$86.45	$86.40
Purchase #4	$54.96	10.812%	$60.9023	$60.90	$60.90	$60.90
Purchase #5	$74.70	12.227%	$83.8336	$83.83	$83.85	$83.80
Purchase #6	$250.66	6.713%	$267.4868	$267.49	$267.50	$267.50
Purchase #7	$85.27	7.568%	$91.7232	$91.72	$91.70	$91.70
7 purchase totals =	$728.11		$788.9499	$788.94	$788.95	$788.90