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	$159.35	5.858%	$168.6847	$168.68	$168.70	$168.70
Purchase #2	$117.99	4.601%	$123.4187	$123.42	$123.40	$123.40
Purchase #3	$201.86	3.102%	$208.1217	$208.12	$208.10	$208.10
Purchase #4	$212.89	13.764%	$242.1922	$242.19	$242.20	$242.20
Purchase #5	$59.64	4.538%	$62.3465	$62.35	$62.35	$62.30
Purchase #6	$98.87	7.363%	$106.1498	$106.15	$106.15	$106.10
Purchase #7	$242.85	10.582%	$268.5484	$268.55	$268.55	$268.50
7 purchase totals =	$1,093.45		$1,179.4620	$1,179.46	$1,179.45	$1,179.30