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	$210.84	5.524%	$222.4868	$222.49	$222.50	$222.50
Purchase #2	$193.31	11.640%	$215.8113	$215.81	$215.80	$215.80
Purchase #3	$143.75	13.754%	$163.5214	$163.52	$163.50	$163.50
Purchase #4	$92.42	3.716%	$95.8543	$95.85	$95.85	$95.90
Purchase #5	$86.29	5.261%	$90.8297	$90.83	$90.85	$90.80
Purchase #6	$21.86	13.179%	$24.7409	$24.74	$24.75	$24.70
Purchase #7	$189.72	7.425%	$203.8067	$203.81	$203.80	$203.80
7 purchase totals =	$938.19		$1,017.0511	$1,017.05	$1,017.05	$1,017.00