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	$178.60	12.154%	$200.307	$200.31	$200.30	$200.30
Purchase #2	$84.32	7.193%	$90.3851	$90.39	$90.40	$90.40
Purchase #3	$42.72	9.387%	$46.7301	$46.73	$46.75	$46.70
Purchase #4	$118.43	8.193%	$128.133	$128.13	$128.15	$128.10
Purchase #5	$52.50	9.672%	$57.5778	$57.58	$57.60	$57.60
Purchase #6	$206.87	4.664%	$216.5184	$216.52	$216.50	$216.50
Purchase #7	$164.96	5.550%	$174.1153	$174.12	$174.10	$174.10
7 purchase totals =	$848.40		$913.7667	$913.78	$913.80	$913.70