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	$31.39	6.469%	$33.4206	$33.42	$33.40	$33.40
Purchase #2	$104.54	9.771%	$114.7546	$114.75	$114.75	$114.80
Purchase #3	$140.99	4.692%	$147.6053	$147.61	$147.60	$147.60
Purchase #4	$84.68	9.750%	$92.9363	$92.94	$92.95	$92.90
Purchase #5	$224.74	13.531%	$255.1496	$255.15	$255.15	$255.10
Purchase #6	$73.27	12.535%	$82.4544	$82.45	$82.45	$82.50
Purchase #7	$61.82	5.309%	$65.102	$65.10	$65.10	$65.10
7 purchase totals =	$721.43		$791.4228	$791.42	$791.40	$791.40