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	$227.31	12.228%	$255.1055	$255.11	$255.10	$255.10
Purchase #2	$95.44	7.620%	$102.7125	$102.71	$102.70	$102.70
Purchase #3	$18.56	8.351%	$20.1099	$20.11	$20.10	$20.10
Purchase #4	$210.85	5.449%	$222.3392	$222.34	$222.35	$222.30
Purchase #5	$208.97	6.504%	$222.5614	$222.56	$222.55	$222.60
Purchase #6	$7.52	4.567%	$7.8634	$7.86	$7.85	$7.90
Purchase #7	$133.52	4.297%	$139.2574	$139.26	$139.25	$139.30
7 purchase totals =	$902.17		$969.9493	$969.95	$969.90	$970.00