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	$66.90	11.768%	$74.7728	$74.77	$74.75	$74.80
Purchase #2	$27.48	10.203%	$30.2838	$30.28	$30.30	$30.30
Purchase #3	$140.77	7.156%	$150.8435	$150.84	$150.85	$150.80
Purchase #4	$90.25	9.718%	$99.0205	$99.02	$99.00	$99.00
Purchase #5	$65.85	10.738%	$72.921	$72.92	$72.90	$72.90
Purchase #6	$6.60	9.242%	$7.21	$7.21	$7.20	$7.20
Purchase #7	$57.56	13.178%	$65.1453	$65.15	$65.15	$65.10
7 purchase totals =	$455.41		$500.1969	$500.19	$500.15	$500.10