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	$74.51	12.847%	$84.0823	$84.08	$84.10	$84.10
Purchase #2	$38.29	6.307%	$40.705	$40.71	$40.70	$40.70
Purchase #3	$109.43	7.385%	$117.5114	$117.51	$117.50	$117.50
Purchase #4	$174.71	12.704%	$196.9052	$196.91	$196.90	$196.90
Purchase #5	$40.47	12.411%	$45.4927	$45.49	$45.50	$45.50
Purchase #6	$159.91	3.546%	$165.5804	$165.58	$165.60	$165.60
Purchase #7	$88.27	6.127%	$93.6783	$93.68	$93.70	$93.70
7 purchase totals =	$685.59		$743.9553	$743.96	$744.00	$744.00