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	$80.70	12.553%	$90.8303	$90.83	$90.85	$90.80
Purchase #2	$68.98	11.351%	$76.8099	$76.81	$76.80	$76.80
Purchase #3	$100.32	9.571%	$109.9216	$109.92	$109.90	$109.90
Purchase #4	$141.88	12.833%	$160.0875	$160.09	$160.10	$160.10
Purchase #5	$209.42	9.205%	$228.6971	$228.70	$228.70	$228.70
Purchase #6	$125.52	4.576%	$131.2638	$131.26	$131.25	$131.30
Purchase #7	$210.36	4.533%	$219.8956	$219.90	$219.90	$219.90
7 purchase totals =	$937.18		$1,017.5058	$1,017.51	$1,017.50	$1,017.50