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	$85.27	4.750%	$89.3203	$89.32	$89.30	$89.30
Purchase #2	$42.43	9.862%	$46.6144	$46.61	$46.60	$46.60
Purchase #3	$20.82	12.445%	$23.411	$23.41	$23.40	$23.40
Purchase #4	$91.99	9.710%	$100.9222	$100.92	$100.90	$100.90
Purchase #5	$197.68	10.746%	$218.9227	$218.92	$218.90	$218.90
Purchase #6	$43.95	5.855%	$46.5233	$46.52	$46.50	$46.50
Purchase #7	$58.28	10.200%	$64.2246	$64.22	$64.20	$64.20
7 purchase totals =	$540.42		$589.9385	$589.92	$589.80	$589.80