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	$150.25	4.165%	$156.5079	$156.51	$156.50	$156.50
Purchase #2	$176.81	7.724%	$190.4668	$190.47	$190.45	$190.50
Purchase #3	$218.33	13.537%	$247.8853	$247.89	$247.90	$247.90
Purchase #4	$96.87	5.582%	$102.2773	$102.28	$102.30	$102.30
Purchase #5	$228.63	11.649%	$255.2631	$255.26	$255.25	$255.30
Purchase #6	$99.71	3.709%	$103.4082	$103.41	$103.40	$103.40
Purchase #7	$236.40	6.396%	$251.5201	$251.52	$251.50	$251.50
7 purchase totals =	$1,207.00		$1,307.3287	$1,307.34	$1,307.30	$1,307.40