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	$248.51	12.813%	$280.3516	$280.35	$280.35	$280.40
Purchase #2	$76.77	9.384%	$83.9741	$83.97	$83.95	$84.00
Purchase #3	$41.47	9.144%	$45.262	$45.26	$45.25	$45.30
Purchase #4	$164.57	5.479%	$173.5868	$173.59	$173.60	$173.60
Purchase #5	$229.71	6.776%	$245.2751	$245.28	$245.30	$245.30
Purchase #6	$45.28	4.447%	$47.2936	$47.29	$47.30	$47.30
Purchase #7	$131.80	8.729%	$143.3048	$143.30	$143.30	$143.30
7 purchase totals =	$938.11		$1,019.0480	$1,019.04	$1,019.05	$1,019.20