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	$25.90	8.669%	$28.1453	$28.15	$28.15	$28.10
Purchase #2	$199.93	13.540%	$227.0005	$227.00	$227.00	$227.00
Purchase #3	$156.88	9.255%	$171.3992	$171.40	$171.40	$171.40
Purchase #4	$177.73	11.649%	$198.4338	$198.43	$198.45	$198.40
Purchase #5	$196.40	10.403%	$216.8315	$216.83	$216.85	$216.80
Purchase #6	$124.34	5.398%	$131.0519	$131.05	$131.05	$131.10
Purchase #7	$52.89	13.152%	$59.8461	$59.85	$59.85	$59.80
7 purchase totals =	$934.07		$1,032.7083	$1,032.71	$1,032.75	$1,032.60