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	$189.35	12.686%	$213.3709	$213.37	$213.35	$213.40
Purchase #2	$49.46	4.845%	$51.8563	$51.86	$51.85	$51.90
Purchase #3	$83.60	8.242%	$90.4903	$90.49	$90.50	$90.50
Purchase #4	$198.89	6.254%	$211.3286	$211.33	$211.35	$211.30
Purchase #5	$131.64	8.104%	$142.3081	$142.31	$142.30	$142.30
Purchase #6	$65.85	11.162%	$73.2002	$73.20	$73.20	$73.20
Purchase #7	$93.85	10.724%	$103.9145	$103.91	$103.90	$103.90
7 purchase totals =	$812.64		$886.4689	$886.47	$886.45	$886.50