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	$226.77	12.813%	$255.826	$255.83	$255.85	$255.80
Purchase #2	$184.59	3.318%	$190.7147	$190.71	$190.70	$190.70
Purchase #3	$158.88	12.308%	$178.435	$178.44	$178.45	$178.40
Purchase #4	$81.56	13.460%	$92.538	$92.54	$92.55	$92.50
Purchase #5	$82.26	8.568%	$89.308	$89.31	$89.30	$89.30
Purchase #6	$179.81	10.732%	$199.1072	$199.11	$199.10	$199.10
Purchase #7	$195.76	11.307%	$217.8946	$217.89	$217.90	$217.90
7 purchase totals =	$1,109.63		$1,223.8235	$1,223.83	$1,223.85	$1,223.70