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	$40.50	7.159%	$43.3994	$43.40	$43.40	$43.40
Purchase #2	$56.83	11.658%	$63.4552	$63.46	$63.45	$63.50
Purchase #3	$23.58	5.495%	$24.8757	$24.88	$24.90	$24.90
Purchase #4	$80.69	12.334%	$90.6423	$90.64	$90.65	$90.60
Purchase #5	$167.82	6.282%	$178.3625	$178.36	$178.35	$178.40
Purchase #6	$228.70	5.599%	$241.5049	$241.50	$241.50	$241.50
Purchase #7	$40.78	8.346%	$44.1835	$44.18	$44.20	$44.20
7 purchase totals =	$638.90		$686.4235	$686.42	$686.45	$686.50