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	$205.47	4.853%	$215.4415	$215.44	$215.45	$215.40
Purchase #2	$89.68	3.473%	$92.7946	$92.79	$92.80	$92.80
Purchase #3	$88.92	13.293%	$100.7401	$100.74	$100.75	$100.70
Purchase #4	$216.52	10.652%	$239.5837	$239.58	$239.60	$239.60
Purchase #5	$33.30	5.608%	$35.1675	$35.17	$35.15	$35.20
Purchase #6	$124.28	8.477%	$134.8152	$134.82	$134.80	$134.80
Purchase #7	$122.72	3.750%	$127.322	$127.32	$127.30	$127.30
7 purchase totals =	$880.89		$945.8646	$945.86	$945.85	$945.80