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	$122.79	10.833%	$136.0918	$136.09	$136.10	$136.10
Purchase #2	$25.91	4.856%	$27.1682	$27.17	$27.15	$27.20
Purchase #3	$150.34	6.795%	$160.5556	$160.56	$160.55	$160.60
Purchase #4	$241.68	6.159%	$256.5651	$256.57	$256.55	$256.60
Purchase #5	$18.90	10.409%	$20.8673	$20.87	$20.85	$20.90
Purchase #6	$168.32	6.502%	$179.2642	$179.26	$179.25	$179.30
Purchase #7	$244.95	12.389%	$275.2969	$275.30	$275.30	$275.30
7 purchase totals =	$972.89		$1,055.8091	$1,055.82	$1,055.75	$1,056.00