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	$177.79	5.680%	$187.8885	$187.89	$187.90	$187.90
Purchase #2	$246.91	9.720%	$270.9097	$270.91	$270.90	$270.90
Purchase #3	$122.69	12.689%	$138.2581	$138.26	$138.25	$138.30
Purchase #4	$176.28	4.758%	$184.6674	$184.67	$184.65	$184.70
Purchase #5	$70.36	11.506%	$78.4556	$78.46	$78.45	$78.50
Purchase #6	$79.84	13.512%	$90.628	$90.63	$90.65	$90.60
Purchase #7	$18.98	10.451%	$20.9636	$20.96	$20.95	$21.00
7 purchase totals =	$892.85		$971.7709	$971.78	$971.75	$971.90