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	$236.60	11.390%	$263.5487	$263.55	$263.55	$263.50
Purchase #2	$38.67	9.702%	$42.4218	$42.42	$42.40	$42.40
Purchase #3	$179.94	11.769%	$201.1171	$201.12	$201.10	$201.10
Purchase #4	$30.96	6.172%	$32.8709	$32.87	$32.85	$32.90
Purchase #5	$81.80	10.183%	$90.1297	$90.13	$90.15	$90.10
Purchase #6	$173.31	3.528%	$179.4244	$179.42	$179.40	$179.40
Purchase #7	$101.76	7.788%	$109.6851	$109.69	$109.70	$109.70
7 purchase totals =	$843.04		$919.1977	$919.20	$919.15	$919.10