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	$57.38	9.454%	$62.8047	$62.80	$62.80	$62.80
Purchase #2	$173.66	11.321%	$193.32	$193.32	$193.30	$193.30
Purchase #3	$109.53	7.642%	$117.9003	$117.90	$117.90	$117.90
Purchase #4	$78.72	8.216%	$85.1876	$85.19	$85.20	$85.20
Purchase #5	$107.30	9.442%	$117.4313	$117.43	$117.45	$117.40
Purchase #6	$84.54	12.387%	$95.012	$95.01	$95.00	$95.00
Purchase #7	$121.41	5.308%	$127.8544	$127.85	$127.85	$127.90
7 purchase totals =	$732.54		$799.5103	$799.50	$799.50	$799.50