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	$27.59	6.687%	$29.4349	$29.43	$29.45	$29.40
Purchase #2	$55.64	11.250%	$61.8995	$61.90	$61.90	$61.90
Purchase #3	$79.45	12.106%	$89.0682	$89.07	$89.05	$89.10
Purchase #4	$170.96	5.541%	$180.4329	$180.43	$180.45	$180.40
Purchase #5	$250.70	11.545%	$279.6433	$279.64	$279.65	$279.60
Purchase #6	$35.59	13.386%	$40.3541	$40.35	$40.35	$40.40
Purchase #7	$142.65	9.874%	$156.7353	$156.74	$156.75	$156.70
7 purchase totals =	$762.58		$837.5682	$837.56	$837.60	$837.50