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	$99.58	3.425%	$102.9906	$102.99	$103.00	$103.00
Purchase #2	$67.96	6.712%	$72.5215	$72.52	$72.50	$72.50
Purchase #3	$137.26	13.108%	$155.252	$155.25	$155.25	$155.30
Purchase #4	$14.37	12.455%	$16.1598	$16.16	$16.15	$16.20
Purchase #5	$177.80	12.786%	$200.5335	$200.53	$200.55	$200.50
Purchase #6	$183.63	3.761%	$190.5363	$190.54	$190.55	$190.50
Purchase #7	$47.89	6.808%	$51.1504	$51.15	$51.15	$51.20
7 purchase totals =	$728.49		$789.1441	$789.14	$789.15	$789.20