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	$234.58	6.563%	$249.9755	$249.98	$250.00	$250.00
Purchase #2	$175.92	3.289%	$181.706	$181.71	$181.70	$181.70
Purchase #3	$98.79	12.208%	$110.8503	$110.85	$110.85	$110.90
Purchase #4	$70.91	11.210%	$78.859	$78.86	$78.85	$78.90
Purchase #5	$246.83	7.805%	$266.0951	$266.10	$266.10	$266.10
Purchase #6	$123.35	4.164%	$128.4863	$128.49	$128.50	$128.50
Purchase #7	$196.38	13.504%	$222.8992	$222.90	$222.90	$222.90
7 purchase totals =	$1,146.76		$1,238.8714	$1,238.89	$1,238.90	$1,239.00