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	$98.31	5.155%	$103.3779	$103.38	$103.40	$103.40
Purchase #2	$131.81	13.854%	$150.071	$150.07	$150.05	$150.10
Purchase #3	$15.78	11.857%	$17.651	$17.65	$17.65	$17.70
Purchase #4	$99.63	7.414%	$107.0166	$107.02	$107.00	$107.00
Purchase #5	$121.38	8.666%	$131.8988	$131.90	$131.90	$131.90
Purchase #6	$121.26	8.295%	$131.3185	$131.32	$131.30	$131.30
Purchase #7	$239.91	4.249%	$250.1038	$250.10	$250.10	$250.10
7 purchase totals =	$828.08		$891.4376	$891.44	$891.40	$891.50