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	$91.30	12.233%	$102.4687	$102.47	$102.45	$102.50
Purchase #2	$35.70	13.255%	$40.432	$40.43	$40.45	$40.40
Purchase #3	$92.59	13.708%	$105.2822	$105.28	$105.30	$105.30
Purchase #4	$59.60	10.492%	$65.8532	$65.85	$65.85	$65.90
Purchase #5	$97.33	3.665%	$100.8971	$100.90	$100.90	$100.90
Purchase #6	$150.51	10.587%	$166.4445	$166.44	$166.45	$166.40
Purchase #7	$249.86	7.123%	$267.6575	$267.66	$267.65	$267.70
7 purchase totals =	$776.89		$849.0352	$849.03	$849.05	$849.10