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	$241.64	5.721%	$255.4642	$255.46	$255.45	$255.50
Purchase #2	$86.95	4.240%	$90.6367	$90.64	$90.65	$90.60
Purchase #3	$232.46	9.450%	$254.4275	$254.43	$254.45	$254.40
Purchase #4	$6.49	7.576%	$6.9817	$6.98	$7.00	$7.00
Purchase #5	$26.82	10.612%	$29.6661	$29.67	$29.65	$29.70
Purchase #6	$104.82	4.862%	$109.9163	$109.92	$109.90	$109.90
Purchase #7	$126.47	12.532%	$142.3192	$142.32	$142.30	$142.30
7 purchase totals =	$825.65		$889.4117	$889.42	$889.40	$889.40