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	$244.27	4.678%	$255.697	$255.70	$255.70	$255.70
Purchase #2	$40.51	11.855%	$45.3125	$45.31	$45.30	$45.30
Purchase #3	$81.97	9.234%	$89.5391	$89.54	$89.55	$89.50
Purchase #4	$49.73	8.195%	$53.8054	$53.81	$53.80	$53.80
Purchase #5	$156.55	8.270%	$169.4967	$169.50	$169.50	$169.50
Purchase #6	$102.76	8.357%	$111.3477	$111.35	$111.35	$111.30
Purchase #7	$135.77	7.267%	$145.6364	$145.64	$145.65	$145.60
7 purchase totals =	$811.56		$870.8348	$870.85	$870.85	$870.70