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	$134.35	6.586%	$143.1983	$143.20	$143.20	$143.20
Purchase #2	$179.72	8.314%	$194.6619	$194.66	$194.65	$194.70
Purchase #3	$166.59	13.418%	$188.943	$188.94	$188.95	$188.90
Purchase #4	$177.94	10.293%	$196.2554	$196.26	$196.25	$196.30
Purchase #5	$137.57	9.462%	$150.5869	$150.59	$150.60	$150.60
Purchase #6	$131.45	8.538%	$142.6732	$142.67	$142.65	$142.70
Purchase #7	$235.97	12.129%	$264.5908	$264.59	$264.60	$264.60
7 purchase totals =	$1,163.59		$1,280.9095	$1,280.91	$1,280.90	$1,281.00