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	$16.74	8.730%	$18.2014	$18.20	$18.20	$18.20
Purchase #2	$194.60	11.244%	$216.4808	$216.48	$216.50	$216.50
Purchase #3	$196.95	10.437%	$217.5057	$217.51	$217.50	$217.50
Purchase #4	$246.80	9.693%	$270.7223	$270.72	$270.70	$270.70
Purchase #5	$53.32	12.398%	$59.9306	$59.93	$59.95	$59.90
Purchase #6	$31.90	6.370%	$33.932	$33.93	$33.95	$33.90
Purchase #7	$210.72	6.280%	$223.9532	$223.95	$223.95	$224.00
7 purchase totals =	$951.03		$1,040.7260	$1,040.72	$1,040.75	$1,040.70