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	$94.79	9.597%	$103.887	$103.89	$103.90	$103.90
Purchase #2	$108.60	13.587%	$123.3555	$123.36	$123.35	$123.40
Purchase #3	$108.48	5.583%	$114.5364	$114.54	$114.55	$114.50
Purchase #4	$147.51	12.596%	$166.0904	$166.09	$166.10	$166.10
Purchase #5	$171.78	13.148%	$194.3656	$194.37	$194.35	$194.40
Purchase #6	$241.49	12.814%	$272.4345	$272.43	$272.45	$272.40
Purchase #7	$26.53	11.502%	$29.5815	$29.58	$29.60	$29.60
7 purchase totals =	$899.18		$1,004.2509	$1,004.26	$1,004.30	$1,004.30