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	$220.60	13.522%	$250.4295	$250.43	$250.45	$250.40
Purchase #2	$175.51	6.225%	$186.4355	$186.44	$186.45	$186.40
Purchase #3	$131.59	6.757%	$140.4815	$140.48	$140.50	$140.50
Purchase #4	$136.52	5.698%	$144.2989	$144.30	$144.30	$144.30
Purchase #5	$75.26	3.532%	$77.9182	$77.92	$77.90	$77.90
Purchase #6	$180.55	13.754%	$205.3828	$205.38	$205.40	$205.40
Purchase #7	$12.74	5.642%	$13.4588	$13.46	$13.45	$13.50
7 purchase totals =	$932.77		$1,018.4052	$1,018.41	$1,018.45	$1,018.40