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	$124.36	9.751%	$136.4863	$136.49	$136.50	$136.50
Purchase #2	$144.95	9.662%	$158.9551	$158.96	$158.95	$159.00
Purchase #3	$100.72	4.786%	$105.5405	$105.54	$105.55	$105.50
Purchase #4	$131.91	9.812%	$144.853	$144.85	$144.85	$144.90
Purchase #5	$132.92	5.787%	$140.6121	$140.61	$140.60	$140.60
Purchase #6	$52.85	3.683%	$54.7965	$54.80	$54.80	$54.80
Purchase #7	$154.98	10.377%	$171.0623	$171.06	$171.05	$171.10
7 purchase totals =	$842.69		$912.3058	$912.31	$912.30	$912.40