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	$176.82	13.434%	$200.574	$200.57	$200.55	$200.60
Purchase #2	$131.75	8.786%	$143.3256	$143.33	$143.35	$143.30
Purchase #3	$110.59	11.432%	$123.2326	$123.23	$123.25	$123.20
Purchase #4	$122.91	12.520%	$138.2983	$138.30	$138.30	$138.30
Purchase #5	$142.32	5.503%	$150.1519	$150.15	$150.15	$150.20
Purchase #6	$128.84	9.119%	$140.5889	$140.59	$140.60	$140.60
Purchase #7	$20.80	5.264%	$21.8949	$21.89	$21.90	$21.90
7 purchase totals =	$834.03		$918.0662	$918.06	$918.10	$918.10