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	$227.47	12.163%	$255.1372	$255.14	$255.15	$255.10
Purchase #2	$240.59	6.160%	$255.4103	$255.41	$255.40	$255.40
Purchase #3	$63.25	8.362%	$68.539	$68.54	$68.55	$68.50
Purchase #4	$215.80	6.794%	$230.4615	$230.46	$230.45	$230.50
Purchase #5	$26.56	10.580%	$29.37	$29.37	$29.35	$29.40
Purchase #6	$134.51	6.219%	$142.8752	$142.88	$142.90	$142.90
Purchase #7	$66.86	5.416%	$70.4811	$70.48	$70.50	$70.50
7 purchase totals =	$975.04		$1,052.2743	$1,052.28	$1,052.30	$1,052.30