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	$85.70	4.211%	$89.3088	$89.31	$89.30	$89.30
Purchase #2	$41.97	7.435%	$45.0905	$45.09	$45.10	$45.10
Purchase #3	$164.34	9.769%	$180.3944	$180.39	$180.40	$180.40
Purchase #4	$55.74	13.471%	$63.2487	$63.25	$63.25	$63.20
Purchase #5	$97.83	12.212%	$109.777	$109.78	$109.80	$109.80
Purchase #6	$123.79	5.204%	$130.232	$130.23	$130.25	$130.20
Purchase #7	$238.79	7.113%	$255.7751	$255.78	$255.80	$255.80
7 purchase totals =	$808.16		$873.8265	$873.83	$873.90	$873.80