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	$134.88	11.648%	$150.5908	$150.59	$150.60	$150.60
Purchase #2	$160.40	12.473%	$180.4067	$180.41	$180.40	$180.40
Purchase #3	$154.60	12.869%	$174.4955	$174.50	$174.50	$174.50
Purchase #4	$118.52	8.414%	$128.4923	$128.49	$128.50	$128.50
Purchase #5	$22.74	13.599%	$25.8324	$25.83	$25.85	$25.80
Purchase #6	$157.45	7.447%	$169.1753	$169.18	$169.20	$169.20
Purchase #7	$141.25	12.196%	$158.4769	$158.48	$158.50	$158.50
7 purchase totals =	$889.84		$987.4699	$987.48	$987.55	$987.50