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	$72.27	12.318%	$81.1722	$81.17	$81.15	$81.20
Purchase #2	$127.37	11.709%	$142.2838	$142.28	$142.30	$142.30
Purchase #3	$210.39	10.828%	$233.171	$233.17	$233.15	$233.20
Purchase #4	$33.32	5.346%	$35.1013	$35.10	$35.10	$35.10
Purchase #5	$95.83	7.857%	$103.3594	$103.36	$103.35	$103.40
Purchase #6	$196.29	8.815%	$213.593	$213.59	$213.60	$213.60
Purchase #7	$106.46	5.791%	$112.6251	$112.63	$112.65	$112.60
7 purchase totals =	$841.93		$921.3058	$921.30	$921.30	$921.40