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	$27.64	8.321%	$29.9399	$29.94	$29.95	$29.90
Purchase #2	$137.79	11.196%	$153.217	$153.22	$153.20	$153.20
Purchase #3	$245.40	8.776%	$266.9363	$266.94	$266.95	$266.90
Purchase #4	$133.52	13.779%	$151.9177	$151.92	$151.90	$151.90
Purchase #5	$186.61	7.208%	$200.0608	$200.06	$200.05	$200.10
Purchase #6	$63.79	5.503%	$67.3004	$67.30	$67.30	$67.30
Purchase #7	$55.73	11.659%	$62.2276	$62.23	$62.25	$62.20
7 purchase totals =	$850.48		$931.5997	$931.61	$931.60	$931.50