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	$30.26	6.528%	$32.2354	$32.24	$32.25	$32.20
Purchase #2	$121.67	4.369%	$126.9858	$126.99	$127.00	$127.00
Purchase #3	$165.46	9.677%	$181.4716	$181.47	$181.45	$181.50
Purchase #4	$163.45	13.227%	$185.0695	$185.07	$185.05	$185.10
Purchase #5	$139.65	11.751%	$156.0603	$156.06	$156.05	$156.10
Purchase #6	$116.82	3.120%	$120.4648	$120.46	$120.45	$120.50
Purchase #7	$45.75	6.834%	$48.8766	$48.88	$48.90	$48.90
7 purchase totals =	$783.06		$851.1640	$851.17	$851.15	$851.30