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	$232.43	3.485%	$240.5302	$240.53	$240.55	$240.50
Purchase #2	$144.41	8.613%	$156.848	$156.85	$156.85	$156.80
Purchase #3	$245.35	13.487%	$278.4404	$278.44	$278.45	$278.40
Purchase #4	$234.35	10.508%	$258.9755	$258.98	$259.00	$259.00
Purchase #5	$25.76	9.284%	$28.1516	$28.15	$28.15	$28.20
Purchase #6	$50.52	7.463%	$54.2903	$54.29	$54.30	$54.30
Purchase #7	$65.88	4.668%	$68.9553	$68.96	$68.95	$69.00
7 purchase totals =	$998.70		$1,086.1913	$1,086.20	$1,086.25	$1,086.20