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	$112.47	13.289%	$127.4161	$127.42	$127.40	$127.40
Purchase #2	$238.85	9.308%	$261.0822	$261.08	$261.10	$261.10
Purchase #3	$246.54	12.128%	$276.4404	$276.44	$276.45	$276.40
Purchase #4	$195.77	6.312%	$208.127	$208.13	$208.15	$208.10
Purchase #5	$73.26	13.734%	$83.3215	$83.32	$83.30	$83.30
Purchase #6	$18.35	12.874%	$20.7124	$20.71	$20.70	$20.70
Purchase #7	$144.74	12.299%	$162.5416	$162.54	$162.55	$162.50
7 purchase totals =	$1,029.98		$1,139.6412	$1,139.64	$1,139.65	$1,139.50