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	$126.25	13.678%	$143.5185	$143.52	$143.50	$143.50
Purchase #2	$206.44	7.663%	$222.2595	$222.26	$222.25	$222.30
Purchase #3	$172.84	4.326%	$180.3171	$180.32	$180.30	$180.30
Purchase #4	$128.48	7.706%	$138.3807	$138.38	$138.40	$138.40
Purchase #5	$177.62	3.288%	$183.4601	$183.46	$183.45	$183.50
Purchase #6	$59.78	12.601%	$67.3129	$67.31	$67.30	$67.30
Purchase #7	$159.83	7.358%	$171.5903	$171.59	$171.60	$171.60
7 purchase totals =	$1,031.24		$1,106.8391	$1,106.84	$1,106.80	$1,106.90