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	$97.88	12.306%	$109.9251	$109.93	$109.95	$109.90
Purchase #2	$81.57	10.125%	$89.829	$89.83	$89.85	$89.80
Purchase #3	$190.80	11.126%	$212.0284	$212.03	$212.05	$212.00
Purchase #4	$131.68	9.188%	$143.7788	$143.78	$143.80	$143.80
Purchase #5	$205.44	3.584%	$212.803	$212.80	$212.80	$212.80
Purchase #6	$118.90	10.599%	$131.5022	$131.50	$131.50	$131.50
Purchase #7	$164.71	7.698%	$177.3894	$177.39	$177.40	$177.40
7 purchase totals =	$990.98		$1,077.2559	$1,077.26	$1,077.35	$1,077.20