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	$86.32	3.590%	$89.4189	$89.42	$89.40	$89.40
Purchase #2	$218.87	13.729%	$248.9187	$248.92	$248.90	$248.90
Purchase #3	$32.56	12.322%	$36.572	$36.57	$36.55	$36.60
Purchase #4	$234.28	10.338%	$258.4999	$258.50	$258.50	$258.50
Purchase #5	$176.70	11.188%	$196.4692	$196.47	$196.45	$196.50
Purchase #6	$94.97	5.326%	$100.0281	$100.03	$100.05	$100.00
Purchase #7	$136.95	7.719%	$147.5212	$147.52	$147.50	$147.50
7 purchase totals =	$980.65		$1,077.4280	$1,077.43	$1,077.35	$1,077.40