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	$121.36	11.346%	$135.1295	$135.13	$135.15	$135.10
Purchase #2	$86.56	6.799%	$92.4452	$92.45	$92.45	$92.40
Purchase #3	$83.66	7.560%	$89.9847	$89.98	$90.00	$90.00
Purchase #4	$242.82	5.311%	$255.7162	$255.72	$255.70	$255.70
Purchase #5	$6.98	3.657%	$7.2353	$7.24	$7.25	$7.20
Purchase #6	$6.69	9.455%	$7.3225	$7.32	$7.30	$7.30
Purchase #7	$95.47	6.233%	$101.4206	$101.42	$101.40	$101.40
7 purchase totals =	$643.54		$689.2540	$689.26	$689.25	$689.10