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	$127.94	8.157%	$138.3761	$138.38	$138.40	$138.40
Purchase #2	$85.37	6.342%	$90.7842	$90.78	$90.80	$90.80
Purchase #3	$35.52	12.805%	$40.0683	$40.07	$40.05	$40.10
Purchase #4	$171.53	12.622%	$193.1805	$193.18	$193.20	$193.20
Purchase #5	$190.81	4.221%	$198.8641	$198.86	$198.85	$198.90
Purchase #6	$204.28	11.436%	$227.6415	$227.64	$227.65	$227.60
Purchase #7	$54.38	12.738%	$61.3069	$61.31	$61.30	$61.30
7 purchase totals =	$869.83		$950.2216	$950.22	$950.25	$950.30