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	$235.48	10.184%	$259.4613	$259.46	$259.45	$259.50
Purchase #2	$225.88	3.611%	$234.0365	$234.04	$234.05	$234.00
Purchase #3	$72.81	8.121%	$78.7229	$78.72	$78.70	$78.70
Purchase #4	$114.58	3.221%	$118.2706	$118.27	$118.25	$118.30
Purchase #5	$44.89	6.290%	$47.7136	$47.71	$47.70	$47.70
Purchase #6	$131.45	3.873%	$136.5411	$136.54	$136.55	$136.50
Purchase #7	$120.45	5.288%	$126.8194	$126.82	$126.80	$126.80
7 purchase totals =	$945.54		$1,001.5654	$1,001.56	$1,001.50	$1,001.50