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	$38.99	5.405%	$41.0974	$41.10	$41.10	$41.10
Purchase #2	$122.67	13.613%	$139.3691	$139.37	$139.35	$139.40
Purchase #3	$64.41	4.740%	$67.463	$67.46	$67.45	$67.50
Purchase #4	$188.83	10.381%	$208.4324	$208.43	$208.45	$208.40
Purchase #5	$53.87	12.158%	$60.4195	$60.42	$60.40	$60.40
Purchase #6	$215.79	8.238%	$233.5668	$233.57	$233.55	$233.60
Purchase #7	$38.94	5.860%	$41.2219	$41.22	$41.20	$41.20
7 purchase totals =	$723.50		$791.5701	$791.57	$791.50	$791.60