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	$29.95	12.793%	$33.7815	$33.78	$33.80	$33.80
Purchase #2	$102.27	10.291%	$112.7946	$112.79	$112.80	$112.80
Purchase #3	$186.40	4.777%	$195.3043	$195.30	$195.30	$195.30
Purchase #4	$61.88	4.732%	$64.8082	$64.81	$64.80	$64.80
Purchase #5	$245.64	4.534%	$256.7773	$256.78	$256.80	$256.80
Purchase #6	$238.69	13.571%	$271.0826	$271.08	$271.10	$271.10
Purchase #7	$246.65	3.408%	$255.0558	$255.06	$255.05	$255.10
7 purchase totals =	$1,111.48		$1,189.6043	$1,189.60	$1,189.65	$1,189.70