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	$118.42	4.163%	$123.3498	$123.35	$123.35	$123.30
Purchase #2	$144.67	9.835%	$158.8983	$158.90	$158.90	$158.90
Purchase #3	$221.67	9.479%	$242.6821	$242.68	$242.70	$242.70
Purchase #4	$114.51	7.624%	$123.2402	$123.24	$123.25	$123.20
Purchase #5	$84.52	5.819%	$89.4382	$89.44	$89.45	$89.40
Purchase #6	$65.35	3.335%	$67.5294	$67.53	$67.55	$67.50
Purchase #7	$68.81	7.669%	$74.087	$74.09	$74.10	$74.10
7 purchase totals =	$817.95		$879.2250	$879.23	$879.30	$879.10