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	$150.54	10.253%	$165.9749	$165.97	$165.95	$166.00
Purchase #2	$123.88	6.394%	$131.8009	$131.80	$131.80	$131.80
Purchase #3	$65.42	10.504%	$72.2917	$72.29	$72.30	$72.30
Purchase #4	$42.69	11.153%	$47.4512	$47.45	$47.45	$47.50
Purchase #5	$217.43	10.358%	$239.9514	$239.95	$239.95	$240.00
Purchase #6	$60.99	10.487%	$67.386	$67.39	$67.40	$67.40
Purchase #7	$66.78	6.390%	$71.0472	$71.05	$71.05	$71.00
7 purchase totals =	$727.73		$795.9033	$795.90	$795.90	$796.00