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	$36.60	8.122%	$39.5727	$39.57	$39.55	$39.60
Purchase #2	$117.62	8.475%	$127.5883	$127.59	$127.60	$127.60
Purchase #3	$172.79	8.809%	$188.0111	$188.01	$188.00	$188.00
Purchase #4	$203.98	4.839%	$213.8506	$213.85	$213.85	$213.90
Purchase #5	$127.74	3.196%	$131.8226	$131.82	$131.80	$131.80
Purchase #6	$136.45	5.260%	$143.6273	$143.63	$143.65	$143.60
Purchase #7	$64.28	5.405%	$67.7543	$67.75	$67.75	$67.80
7 purchase totals =	$859.46		$912.2269	$912.22	$912.20	$912.30