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	$133.33	13.170%	$150.8896	$150.89	$150.90	$150.90
Purchase #2	$47.56	4.845%	$49.8643	$49.86	$49.85	$49.90
Purchase #3	$196.33	13.349%	$222.5381	$222.54	$222.55	$222.50
Purchase #4	$174.30	3.208%	$179.8915	$179.89	$179.90	$179.90
Purchase #5	$72.62	10.748%	$80.4252	$80.43	$80.45	$80.40
Purchase #6	$238.92	5.739%	$252.6316	$252.63	$252.65	$252.60
Purchase #7	$69.34	8.203%	$75.028	$75.03	$75.05	$75.00
7 purchase totals =	$932.40		$1,011.2683	$1,011.27	$1,011.35	$1,011.20