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	$36.39	8.815%	$39.5978	$39.60	$39.60	$39.60
Purchase #2	$160.25	5.220%	$168.6151	$168.62	$168.60	$168.60
Purchase #3	$180.28	13.853%	$205.2542	$205.25	$205.25	$205.30
Purchase #4	$180.77	13.644%	$205.4343	$205.43	$205.45	$205.40
Purchase #5	$183.75	9.141%	$200.5466	$200.55	$200.55	$200.50
Purchase #6	$42.43	3.190%	$43.7835	$43.78	$43.80	$43.80
Purchase #7	$202.74	3.195%	$209.2175	$209.22	$209.20	$209.20
7 purchase totals =	$986.61		$1,072.4490	$1,072.45	$1,072.45	$1,072.40