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	$49.97	5.820%	$52.8783	$52.88	$52.90	$52.90
Purchase #2	$126.98	13.782%	$144.4804	$144.48	$144.50	$144.50
Purchase #3	$217.68	7.584%	$234.1889	$234.19	$234.20	$234.20
Purchase #4	$122.74	6.850%	$131.1477	$131.15	$131.15	$131.10
Purchase #5	$50.76	9.472%	$55.568	$55.57	$55.55	$55.60
Purchase #6	$169.41	4.201%	$176.5269	$176.53	$176.55	$176.50
Purchase #7	$226.88	12.739%	$255.7822	$255.78	$255.80	$255.80
7 purchase totals =	$964.42		$1,050.5724	$1,050.58	$1,050.65	$1,050.60