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	$73.70	6.476%	$78.4728	$78.47	$78.45	$78.50
Purchase #2	$153.64	3.429%	$158.9083	$158.91	$158.90	$158.90
Purchase #3	$119.32	7.340%	$128.0781	$128.08	$128.10	$128.10
Purchase #4	$144.48	5.851%	$152.9335	$152.93	$152.95	$152.90
Purchase #5	$142.25	10.473%	$157.1478	$157.15	$157.15	$157.10
Purchase #6	$186.55	12.299%	$209.4938	$209.49	$209.50	$209.50
Purchase #7	$114.79	4.397%	$119.8373	$119.84	$119.85	$119.80
7 purchase totals =	$934.73		$1,004.8716	$1,004.87	$1,004.90	$1,004.80