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	$18.57	10.569%	$20.5327	$20.53	$20.55	$20.50
Purchase #2	$115.86	12.266%	$130.0714	$130.07	$130.05	$130.10
Purchase #3	$13.86	12.548%	$15.5992	$15.60	$15.60	$15.60
Purchase #4	$134.56	4.553%	$140.6865	$140.69	$140.70	$140.70
Purchase #5	$193.88	9.272%	$211.8566	$211.86	$211.85	$211.90
Purchase #6	$85.31	7.276%	$91.5172	$91.52	$91.50	$91.50
Purchase #7	$214.45	12.532%	$241.3249	$241.32	$241.30	$241.30
7 purchase totals =	$776.49		$851.5885	$851.59	$851.55	$851.60