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	$71.55	10.794%	$79.2731	$79.27	$79.25	$79.30
Purchase #2	$134.79	13.199%	$152.5809	$152.58	$152.60	$152.60
Purchase #3	$234.96	9.860%	$258.1271	$258.13	$258.15	$258.10
Purchase #4	$214.40	9.403%	$234.56	$234.56	$234.55	$234.60
Purchase #5	$126.39	4.221%	$131.7249	$131.72	$131.70	$131.70
Purchase #6	$202.40	8.418%	$219.438	$219.44	$219.45	$219.40
Purchase #7	$164.78	9.203%	$179.9447	$179.94	$179.95	$179.90
7 purchase totals =	$1,149.27		$1,255.6487	$1,255.64	$1,255.65	$1,255.60