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	$98.82	10.211%	$108.9105	$108.91	$108.90	$108.90
Purchase #2	$80.83	12.643%	$91.0493	$91.05	$91.05	$91.00
Purchase #3	$209.26	10.425%	$231.0754	$231.08	$231.10	$231.10
Purchase #4	$115.70	11.343%	$128.8239	$128.82	$128.80	$128.80
Purchase #5	$89.71	13.192%	$101.5445	$101.54	$101.55	$101.50
Purchase #6	$29.69	4.749%	$31.1	$31.10	$31.10	$31.10
Purchase #7	$246.89	5.269%	$259.8986	$259.90	$259.90	$259.90
7 purchase totals =	$870.90		$952.4022	$952.40	$952.40	$952.30