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	$114.34	11.684%	$127.6995	$127.70	$127.70	$127.70
Purchase #2	$112.97	9.151%	$123.3079	$123.31	$123.30	$123.30
Purchase #3	$140.65	13.790%	$160.0456	$160.05	$160.05	$160.00
Purchase #4	$48.27	7.199%	$51.745	$51.75	$51.75	$51.70
Purchase #5	$85.42	8.391%	$92.5876	$92.59	$92.60	$92.60
Purchase #6	$98.46	10.823%	$109.1163	$109.12	$109.10	$109.10
Purchase #7	$97.66	8.333%	$105.798	$105.80	$105.80	$105.80
7 purchase totals =	$697.77		$770.2999	$770.32	$770.30	$770.20