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	$179.35	4.594%	$187.5893	$187.59	$187.60	$187.60
Purchase #2	$98.67	4.552%	$103.1615	$103.16	$103.15	$103.20
Purchase #3	$77.63	8.550%	$84.2674	$84.27	$84.25	$84.30
Purchase #4	$166.31	4.435%	$173.6858	$173.69	$173.70	$173.70
Purchase #5	$78.81	4.517%	$82.3698	$82.37	$82.35	$82.40
Purchase #6	$46.93	8.219%	$50.7872	$50.79	$50.80	$50.80
Purchase #7	$80.53	11.201%	$89.5502	$89.55	$89.55	$89.60
7 purchase totals =	$728.23		$771.4112	$771.42	$771.40	$771.60