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	$32.81	12.418%	$36.8843	$36.88	$36.90	$36.90
Purchase #2	$246.43	13.670%	$280.117	$280.12	$280.10	$280.10
Purchase #3	$100.85	10.286%	$111.2234	$111.22	$111.20	$111.20
Purchase #4	$30.42	7.772%	$32.7842	$32.78	$32.80	$32.80
Purchase #5	$204.59	4.218%	$213.2196	$213.22	$213.20	$213.20
Purchase #6	$109.59	10.287%	$120.8635	$120.86	$120.85	$120.90
Purchase #7	$197.63	12.784%	$222.895	$222.90	$222.90	$222.90
7 purchase totals =	$922.32		$1,017.9870	$1,017.98	$1,017.95	$1,018.00