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	$79.96	13.252%	$90.5563	$90.56	$90.55	$90.60
Purchase #2	$208.78	4.390%	$217.9454	$217.95	$217.95	$217.90
Purchase #3	$152.58	7.550%	$164.0998	$164.10	$164.10	$164.10
Purchase #4	$218.73	6.661%	$233.2996	$233.30	$233.30	$233.30
Purchase #5	$142.43	11.859%	$159.3208	$159.32	$159.30	$159.30
Purchase #6	$11.80	13.575%	$13.4019	$13.40	$13.40	$13.40
Purchase #7	$99.69	9.584%	$109.2443	$109.24	$109.25	$109.20
7 purchase totals =	$913.97		$987.8681	$987.87	$987.85	$987.80