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	$104.86	6.531%	$111.7084	$111.71	$111.70	$111.70
Purchase #2	$166.81	9.758%	$183.0873	$183.09	$183.10	$183.10
Purchase #3	$186.87	6.746%	$199.4763	$199.48	$199.50	$199.50
Purchase #4	$182.58	7.729%	$196.6916	$196.69	$196.70	$196.70
Purchase #5	$126.77	5.608%	$133.8793	$133.88	$133.90	$133.90
Purchase #6	$145.56	10.424%	$160.7332	$160.73	$160.75	$160.70
Purchase #7	$95.94	9.524%	$105.0773	$105.08	$105.10	$105.10
7 purchase totals =	$1,009.39		$1,090.6534	$1,090.66	$1,090.75	$1,090.70