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	$72.42	13.144%	$81.9389	$81.94	$81.95	$81.90
Purchase #2	$37.35	12.806%	$42.133	$42.13	$42.15	$42.10
Purchase #3	$205.27	13.571%	$233.1272	$233.13	$233.15	$233.10
Purchase #4	$104.89	9.261%	$114.6039	$114.60	$114.60	$114.60
Purchase #5	$162.29	8.512%	$176.1041	$176.10	$176.10	$176.10
Purchase #6	$76.50	4.796%	$80.1689	$80.17	$80.15	$80.20
Purchase #7	$249.60	3.432%	$258.1663	$258.17	$258.15	$258.20
7 purchase totals =	$908.32		$986.2423	$986.24	$986.25	$986.20