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	$242.93	10.675%	$268.8628	$268.86	$268.85	$268.90
Purchase #2	$37.82	6.836%	$40.4054	$40.41	$40.40	$40.40
Purchase #3	$185.78	6.184%	$197.2686	$197.27	$197.25	$197.30
Purchase #4	$81.60	9.510%	$89.3602	$89.36	$89.35	$89.40
Purchase #5	$86.96	5.139%	$91.4289	$91.43	$91.45	$91.40
Purchase #6	$137.91	11.279%	$153.4649	$153.46	$153.45	$153.50
Purchase #7	$90.47	13.320%	$102.5206	$102.52	$102.50	$102.50
7 purchase totals =	$863.47		$943.3114	$943.31	$943.25	$943.40