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	$215.90	4.476%	$225.5637	$225.56	$225.55	$225.60
Purchase #2	$50.55	6.466%	$53.8186	$53.82	$53.80	$53.80
Purchase #3	$55.76	6.389%	$59.3225	$59.32	$59.30	$59.30
Purchase #4	$180.32	8.367%	$195.4074	$195.41	$195.40	$195.40
Purchase #5	$250.97	11.365%	$279.4927	$279.49	$279.50	$279.50
Purchase #6	$54.52	3.676%	$56.5242	$56.52	$56.50	$56.50
Purchase #7	$8.96	13.851%	$10.201	$10.20	$10.20	$10.20
7 purchase totals =	$816.98		$880.3301	$880.32	$880.25	$880.30