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	$78.51	6.461%	$83.5825	$83.58	$83.60	$83.60
Purchase #2	$138.52	3.872%	$143.8835	$143.88	$143.90	$143.90
Purchase #3	$142.49	7.740%	$153.5187	$153.52	$153.50	$153.50
Purchase #4	$103.87	5.799%	$109.8934	$109.89	$109.90	$109.90
Purchase #5	$57.74	3.195%	$59.5848	$59.58	$59.60	$59.60
Purchase #6	$246.34	10.667%	$272.6171	$272.62	$272.60	$272.60
Purchase #7	$10.93	5.184%	$11.4966	$11.50	$11.50	$11.50
7 purchase totals =	$778.40		$834.5766	$834.57	$834.60	$834.60