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	$52.80	12.772%	$59.5436	$59.54	$59.55	$59.50
Purchase #2	$143.55	4.230%	$149.6222	$149.62	$149.60	$149.60
Purchase #3	$11.55	9.303%	$12.6245	$12.62	$12.60	$12.60
Purchase #4	$206.59	3.265%	$213.3352	$213.34	$213.35	$213.30
Purchase #5	$89.37	11.143%	$99.3285	$99.33	$99.35	$99.30
Purchase #6	$58.90	11.722%	$65.8043	$65.80	$65.80	$65.80
Purchase #7	$68.85	13.457%	$78.1151	$78.12	$78.10	$78.10
7 purchase totals =	$631.61		$678.3734	$678.37	$678.35	$678.20