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	$5.57	4.236%	$5.8059	$5.81	$5.80	$5.80
Purchase #2	$127.71	12.273%	$143.3838	$143.38	$143.40	$143.40
Purchase #3	$164.43	11.773%	$183.7883	$183.79	$183.80	$183.80
Purchase #4	$201.68	10.755%	$223.3707	$223.37	$223.35	$223.40
Purchase #5	$209.26	12.405%	$235.2187	$235.22	$235.20	$235.20
Purchase #6	$52.38	13.357%	$59.3764	$59.38	$59.40	$59.40
Purchase #7	$97.43	12.389%	$109.5006	$109.50	$109.50	$109.50
7 purchase totals =	$858.46		$960.4444	$960.45	$960.45	$960.50