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	$157.81	8.380%	$171.0345	$171.03	$171.05	$171.00
Purchase #2	$164.83	12.820%	$185.9612	$185.96	$185.95	$186.00
Purchase #3	$247.73	12.572%	$278.8746	$278.87	$278.85	$278.90
Purchase #4	$6.56	4.631%	$6.8638	$6.86	$6.85	$6.90
Purchase #5	$80.77	12.162%	$90.5932	$90.59	$90.60	$90.60
Purchase #6	$134.53	8.132%	$145.47	$145.47	$145.45	$145.50
Purchase #7	$135.85	3.235%	$140.2447	$140.24	$140.25	$140.20
7 purchase totals =	$928.08		$1,019.0420	$1,019.02	$1,019.00	$1,019.10