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	$6.69	9.358%	$7.3161	$7.32	$7.30	$7.30
Purchase #2	$46.84	13.500%	$53.1634	$53.16	$53.15	$53.20
Purchase #3	$116.77	10.381%	$128.8919	$128.89	$128.90	$128.90
Purchase #4	$85.40	3.856%	$88.693	$88.69	$88.70	$88.70
Purchase #5	$138.67	6.814%	$148.119	$148.12	$148.10	$148.10
Purchase #6	$240.86	8.854%	$262.1857	$262.19	$262.20	$262.20
Purchase #7	$82.74	8.699%	$89.9376	$89.94	$89.95	$89.90
7 purchase totals =	$717.97		$778.3067	$778.31	$778.30	$778.30