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	$249.63	8.116%	$269.89	$269.89	$269.90	$269.90
Purchase #2	$19.75	5.588%	$20.8536	$20.85	$20.85	$20.90
Purchase #3	$73.97	5.771%	$78.2388	$78.24	$78.25	$78.20
Purchase #4	$53.37	8.255%	$57.7757	$57.78	$57.80	$57.80
Purchase #5	$29.58	5.116%	$31.0933	$31.09	$31.10	$31.10
Purchase #6	$190.87	6.855%	$203.9541	$203.95	$203.95	$204.00
Purchase #7	$140.85	13.658%	$160.0873	$160.09	$160.10	$160.10
7 purchase totals =	$758.02		$821.8928	$821.89	$821.95	$822.00