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	$125.78	10.858%	$139.4372	$139.44	$139.45	$139.40
Purchase #2	$172.51	5.547%	$182.0791	$182.08	$182.10	$182.10
Purchase #3	$89.67	11.312%	$99.8135	$99.81	$99.80	$99.80
Purchase #4	$122.93	6.330%	$130.7115	$130.71	$130.70	$130.70
Purchase #5	$85.81	5.216%	$90.2858	$90.29	$90.30	$90.30
Purchase #6	$100.26	11.535%	$111.825	$111.83	$111.85	$111.80
Purchase #7	$183.26	9.533%	$200.7302	$200.73	$200.75	$200.70
7 purchase totals =	$880.22		$954.8823	$954.89	$954.95	$954.80