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	$61.87	13.276%	$70.0839	$70.08	$70.10	$70.10
Purchase #2	$229.60	10.533%	$253.7838	$253.78	$253.80	$253.80
Purchase #3	$195.89	3.706%	$203.1497	$203.15	$203.15	$203.10
Purchase #4	$169.49	7.104%	$181.5306	$181.53	$181.55	$181.50
Purchase #5	$101.75	11.594%	$113.5469	$113.55	$113.55	$113.50
Purchase #6	$82.30	5.473%	$86.8043	$86.80	$86.80	$86.80
Purchase #7	$89.29	12.519%	$100.4682	$100.47	$100.45	$100.50
7 purchase totals =	$930.19		$1,009.3674	$1,009.36	$1,009.40	$1,009.30