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	$50.54	13.506%	$57.3659	$57.37	$57.35	$57.40
Purchase #2	$19.98	12.401%	$22.4577	$22.46	$22.45	$22.50
Purchase #3	$116.49	9.780%	$127.8827	$127.88	$127.90	$127.90
Purchase #4	$111.94	4.339%	$116.7971	$116.80	$116.80	$116.80
Purchase #5	$38.62	7.763%	$41.6181	$41.62	$41.60	$41.60
Purchase #6	$55.66	7.115%	$59.6202	$59.62	$59.60	$59.60
Purchase #7	$150.42	6.500%	$160.1973	$160.20	$160.20	$160.20
7 purchase totals =	$543.65		$585.9390	$585.95	$585.90	$586.00