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	$62.54	8.172%	$67.6508	$67.65	$67.65	$67.70
Purchase #2	$127.62	9.262%	$139.4402	$139.44	$139.45	$139.40
Purchase #3	$6.83	12.867%	$7.7088	$7.71	$7.70	$7.70
Purchase #4	$110.92	4.829%	$116.2763	$116.28	$116.30	$116.30
Purchase #5	$136.36	6.144%	$144.738	$144.74	$144.75	$144.70
Purchase #6	$119.40	3.511%	$123.5921	$123.59	$123.60	$123.60
Purchase #7	$58.33	3.729%	$60.5051	$60.51	$60.50	$60.50
7 purchase totals =	$622.00		$659.9113	$659.92	$659.95	$659.90