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	$54.25	4.174%	$56.5144	$56.51	$56.50	$56.50
Purchase #2	$122.26	13.258%	$138.4692	$138.47	$138.45	$138.50
Purchase #3	$179.85	3.465%	$186.0818	$186.08	$186.10	$186.10
Purchase #4	$55.94	12.263%	$62.7999	$62.80	$62.80	$62.80
Purchase #5	$85.80	4.393%	$89.5692	$89.57	$89.55	$89.60
Purchase #6	$208.46	6.757%	$222.5456	$222.55	$222.55	$222.50
Purchase #7	$246.84	11.184%	$274.4466	$274.45	$274.45	$274.40
7 purchase totals =	$953.40		$1,030.4267	$1,030.43	$1,030.40	$1,030.40