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	$29.56	10.370%	$32.6254	$32.63	$32.65	$32.60
Purchase #2	$198.39	7.792%	$213.8485	$213.85	$213.85	$213.80
Purchase #3	$103.93	9.460%	$113.7618	$113.76	$113.75	$113.80
Purchase #4	$113.93	11.678%	$127.2347	$127.23	$127.25	$127.20
Purchase #5	$121.47	4.638%	$127.1038	$127.10	$127.10	$127.10
Purchase #6	$239.66	10.412%	$264.6134	$264.61	$264.60	$264.60
Purchase #7	$243.32	6.526%	$259.1991	$259.20	$259.20	$259.20
7 purchase totals =	$1,050.26		$1,138.3867	$1,138.38	$1,138.40	$1,138.30