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	$83.41	4.697%	$87.3278	$87.33	$87.35	$87.30
Purchase #2	$220.53	10.112%	$242.83	$242.83	$242.85	$242.80
Purchase #3	$88.69	13.310%	$100.4946	$100.49	$100.50	$100.50
Purchase #4	$245.61	7.340%	$263.6378	$263.64	$263.65	$263.60
Purchase #5	$42.69	8.698%	$46.4032	$46.40	$46.40	$46.40
Purchase #6	$134.45	3.736%	$139.4731	$139.47	$139.45	$139.50
Purchase #7	$119.57	6.708%	$127.5908	$127.59	$127.60	$127.60
7 purchase totals =	$934.95		$1,007.7573	$1,007.75	$1,007.80	$1,007.70