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	$12.31	9.753%	$13.5106	$13.51	$13.50	$13.50
Purchase #2	$164.75	12.485%	$185.319	$185.32	$185.30	$185.30
Purchase #3	$217.34	8.286%	$235.3488	$235.35	$235.35	$235.30
Purchase #4	$27.76	6.666%	$29.6105	$29.61	$29.60	$29.60
Purchase #5	$78.42	12.630%	$88.3244	$88.32	$88.30	$88.30
Purchase #6	$144.69	7.259%	$155.193	$155.19	$155.20	$155.20
Purchase #7	$196.55	9.585%	$215.3893	$215.39	$215.40	$215.40
7 purchase totals =	$841.82		$922.6956	$922.69	$922.65	$922.60