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	$34.40	11.811%	$38.463	$38.46	$38.45	$38.50
Purchase #2	$134.82	13.729%	$153.3294	$153.33	$153.35	$153.30
Purchase #3	$13.27	12.239%	$14.8941	$14.89	$14.90	$14.90
Purchase #4	$22.46	8.558%	$24.3821	$24.38	$24.40	$24.40
Purchase #5	$31.44	13.745%	$35.7614	$35.76	$35.75	$35.80
Purchase #6	$19.51	9.872%	$21.436	$21.44	$21.45	$21.40
Purchase #7	$177.60	4.485%	$185.5654	$185.57	$185.55	$185.60
7 purchase totals =	$433.50		$473.8314	$473.83	$473.85	$473.90