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	$135.77	6.722%	$144.8965	$144.90	$144.90	$144.90
Purchase #2	$55.81	9.854%	$61.3095	$61.31	$61.30	$61.30
Purchase #3	$154.52	10.703%	$171.0583	$171.06	$171.05	$171.10
Purchase #4	$164.94	13.822%	$187.738	$187.74	$187.75	$187.70
Purchase #5	$242.66	10.632%	$268.4596	$268.46	$268.45	$268.50
Purchase #6	$169.37	5.745%	$179.1003	$179.10	$179.10	$179.10
Purchase #7	$130.34	13.845%	$148.3856	$148.39	$148.40	$148.40
7 purchase totals =	$1,053.41		$1,160.9478	$1,160.96	$1,160.95	$1,161.00