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	$65.62	8.506%	$71.2016	$71.20	$71.20	$71.20
Purchase #2	$24.85	9.623%	$27.2413	$27.24	$27.25	$27.20
Purchase #3	$160.58	4.779%	$168.2541	$168.25	$168.25	$168.30
Purchase #4	$69.88	12.418%	$78.5577	$78.56	$78.55	$78.60
Purchase #5	$143.39	8.662%	$155.8104	$155.81	$155.80	$155.80
Purchase #6	$137.84	11.863%	$154.192	$154.19	$154.20	$154.20
Purchase #7	$166.73	6.781%	$178.036	$178.04	$178.05	$178.00
7 purchase totals =	$768.89		$833.2931	$833.29	$833.30	$833.30